The invention relates to a method for quantitatively detecting polytypes of chrysophanol and emodin in rhubarb and a compound preparation of rhubarb. The method is characterized by integrating methyl extraction and acid hydrolysis into one step; eliminating steps of extraction by poisonous solvents such as trichloromethane and the like, drying by vaporization and the like; and reducing the pre-processing time from original 10 to 15 hours to 0.5 hour, along with high efficiency, low cost and little pollution. By studying components and ratios of the flowing phase, acetonitrile-methyl alcohol-0.1 percent phosphoric acid (the mixing ratio is n 40-45:20-27:38-30) replaces methyl alcohol-0.1 percent phosphoric acid (the mixing ratio is 85:15) as the flowing phase, the problem of difficultly inidentifying coating impurity peaks of the emodin is solved and the correctness of the detection result is ensured. The chrysophanol and the emodin are taken as detection indexes, the same flowing phase is used, and the chrysophanol and the emodin in total, ionization and combined anthraqunione in the preparation are detected at the same. The method has the advantages of combining the detection indexes and the efficacy of the preparation for the first time, improving the scientificity and rationality of the quality control indexes, and being suitably used for various preparations containing the rhubarb, along with simpleness, quickness and accuracy.