The quantitative determination of the mass fractions of precipitates in steels is very difficult using traditional materials characterization techniques.The Rietveld full-pattern fitting algo-rithm was introduced to solve this problem.The precipitated multicomponents\'mass fraction of M_3C,MC,M_7C_3 and M_(23)C_6 were evaluated precisely and relatively quickly.It is found evolution of carbides apparently occurs during tempering at high temperatures,and a two-step transformation mechanism is proposed for M_7C_3 during early tempering treatment.The method is an effective way on the investi-gation of precipitation kinetics,which may play a promising role in propertities\'enhancement and design of the heat-resistant steels.