【正文】 ements, can be used offline test the openloop pensation technology to be amended and pensation, to reduce, to the purpose of enhanced precision machine tools. Random error with a random, must be used online test closedloop pensation approach to the elimination of random errors on the machining accuracy of the method of measuring instrument for measuring the environment, demanding and difficult to promote. 2 Geometric Error Compensation Technology For the different types of errors, the implementation of error pensation can be divided into two broad categories. Random error pensation request online measurement, the error detection device directly installed on the machine, in machine work, realtime position measurement error of the corresponding value of the value of realtime with this error on processing instructions be amended. Random error pensation of machine tools does not require the nature of the error can be the same time machine random error and systematic error pensation. But requires a plete set of highprecision measuring devices and other related equipment, the cost is too high, poor economic returns. [4] to the line of temperature measurement and pensation, failed to achieve practical application. Systematic error pensation is the appropriate instrument to use in advance of the testing machine, namely through the offline measurement to be the location of machine tool workspace mand error values, use them as a function of machine tool coordinates. Machine work, according to processing the coordinates of points, adjusting the corresponding error values to be amended. Better stability of the machine required to ensure the certainty of machine errors, in order to facilitate the amendment, after pensated depends on the accuracy of machine tools, machine tool repeatability and environmental conditions change. CNC Machine Tool Under normal circumstances, repeat accuracy is much higher than its space integrated error, so the system error pensation can effectively improve the accuracy of machine tools, and even can improve the accuracy of machine rating. So far, at home and abroad on the system error pensation methods are many, can be divided into the following methods: Synthesis of singleerror pensation method The pensation method is based on the formula for the theoretical basis for the synthesis error, first measured by direct measurement of the individual machines the value of the original error from the error formula for the calculation of pensation point of synthesis error ponents in order to achieve error pensation of machine tools. Pairs of coordinate measuring machine position error measurement was undoubtedly the Leete, the use of triangular geometric relations derived axes of machine tool error of the representation, without considering the impact of the corner. Earlier for error pensation should be Hocken professor, for the model Moore 5Z (1) of the coordinate measuring machine, 16 hours, measured a large number of points within the working space of the error, in the process taking into account the temperature affected and leastsquares method using the error model parameters were identified. As the machine movement position signal obtained directly from the laser interferometer, taking into account angles and straightness error of the impact of access to more satisfactory results. 1985 G. Zhang successfully carried out on the coordinate measuring machine error pensation. Measuring the flatness error table, in addition to larger values in the table edge, the other less than 1μm, verify the reliability of the rigid body assumption. Use of laser interferometer and measured the level of the 21 errors were, by a linear coordinate transformation for the error synthesis, and implementation of error pensation. Measured results show that XY plane, pensation ago, at all measurement points in the margin of error is greater than 20μm point accounted for 20% in pensation, not more than 20% of the point of error is greater than 2μm, that prec ision can be improved by nearly 10 times. In addition to the error pensa