Adding diesel into expanded ammonium nitrate explosive could decrease the return fine rate,but which also decreased the explosive performance. Based on the basic theory and scientific tests of explosive explosion, the relationship between the diesel ratio and the explosive performance,as well as the return fine rate was studied. At the same time,the relationship curves were drawn. Finally,by discussing the comprehensive relationship,the method to determine the optimal diesel ratio was obtained. The results showed that,with the increase of diesel ratio,the oxy-gen balance,heat of explosive and detonation velocity were decreased;the return fine rate curve was divided into three phases as AB( decline obviously),BC( not remarkably)and CD( maintain);the diesel ratio should be less than 10%;when qmax was in CD,the diesel fuel ratio should be taken as the value of C;when it was in BC,which should be taken as close to the value of B;and the value of qmax should be taken when it was i