【正文】 actors to mining accidents, we can distinguish the primary from the secondary． We can take some measures such as strengthening ventilation, installing air conditioner, eliminating noisy devices etc to improve underground environment so as to improve mining safety and ensure workers’ safety and sustained efficient production． 5． Grey entropy, synthetic evaluation on safety of mining faces 10 5． 1． Grey entropy Suppose a finite discrete sequence X={xi | i=1,2,……,n},grey entropy of sequence X is defined by l n xi xiH (X ) n1i??? (2) If xi=0,let xi ln xi=0 5． 2． Balanced degree Grey entropy is the measure to balance degree of elements in discrete sequence X in terms of grey entropy increase theorem[7]． The greater grey entropy is the more balanced the discrete sequence is． For a discrete sequence with n elements the maximum entropy is a constant ln n which is only relevant with the number, of elements in sequence when all elements are equal． Thus, balanced degree of sequence can be defined by B=H(X)/Hm (3) Where Hm is the maximum grey entropy． 5． 3． Grey correlative degree Grey correlative degree is the measure to adjacent degree between the reference sequence and relative sequence． It can be calculated by correlative coefficients[8]． The correlative coefficient can be calculated by the following equation． ikkkiikkikkkiikkkii vvm a xm a xvvvm a xm a xvvm i nm i nkL ????????? v）（ (4) Where ρ is distinguished coefficient, it is in the range from 0 to 11 1． Usually it is 0． 5． Grey correlative degree can be expressed as． ??? n1kioi kLn1r ）（ (5) Where oir is grey correlative degree between the reference sequence and the thi relative sequence． 5． 4． Model of multilevel grey entropy synthetic evaluation If the evaluation indices lie in different levels． We should apply the model of multilevel grey entropy synthetic evaluation ． Multilevel evaluation model is similar to single level evaluation model ． The secondorder evaluation results from the firstorder evaluation matrix． The evaluation result matrix can be obtained by weight vector and the evaluation matrix in view of the significance difference of indices in the first level． It can be expressed by W=A2W (6) where 2W is the balanced adjacent degree matrix． 5． 5． Synthetic evaluation on mining faces in Xinzhuang coal mine Table 1 shows evaluation indices and original data of mining faces in Xinzhuang coal mine． At first, the secondorder synthetic evaluations are carried out respectively． The process of evaluation is omitted． The evaluation results are shown in Table 2． Table 1 Original data of mining faces Evaluation index e1 e2 12 man machine environment Average age/a Length of service/a Average length of education/a Average professional training Time/d 112 115 Perfect rate/% Rate for maintenance/% Failure rate/% Temperature/℃ Humidity /% Yawp/dB(A) Illumination/Ix Gas/% 92 90 102 95 95 83 Table 2 the secondorder evaluation results Evaluation index Balanced adjacent degree e1 e2 Man Machine Environment The secondorder evaluation results form the firstorder evaluation matrix ． The weights of firstlevel indices call be calculated by AHP． According to ,the synthetic evaluation results can be expressed as following． ?????????????) ( 0 . 6 5WAW 2 (7) According to evaluation rules, el is better than e2． We can draw some useful conclusions from the evaluation on mining faces ． During the secondorder evaluation, we can find out some problems existing in man、machine and environment of mining faces． 13 6． Conclusion The article analyzes deeply man、 machine and environment of fully mechanized mining face system． Some useful conclusions are drawn out． The existing problems are pointed out． The corresponding countermeasures are put forward． These conclusions have been applied in Xinzhuang coal mine． Furthermore, safety of fully mechanized mining face has been improved greatly． References [1]State Administration of Coal Mine Safety． Comprehensive analysis on coun