Abstract: Reworked sedimentary materials were simulated by mixing of high and low rank coals in various proportions,so as to evaluate the variation of T_max from Rock-Eval pyrolysis.The results indicate that(1) once the low rank coal is mixed with high rank coal,the T_max is close to that of the low rank coal,whatever the mixing ratio is;(2) care must be taken for reworked samples,especially for organic materials with high maturity,even dealing with a very small amount of sample mixing;(3) Because of the fast dropping of T_max after increasing mixed ratio of low rank coal,the correlation of R_o and T_max is quite different from the linear trend possessed by type-Ⅲ kerogen.