The invention discloses a preparation method of lithospermum phenolic acids, adjuvant resistant to early pregnancy. The method comprises the steps of smashing natural lithospermum, extracting for two times (1.5 hours for each time) through water, concentrating extracted solution in decompression mode, enabling the extracted solution to go through macroporous resin, washing the extracted solution with ethanol to be colorless, eluting with the ethanol, collecting, continuously concentrating, washing concentrate in MCI gel CHP20P column stilled water until occurrence of chemical compound dipotassium salt, eluting with the ethanol, collecting the chemical compound dipotassium salt and 30% ethanol eluting part, and obtaining eluant of lithospermum phenolic acids effective parts. The lithospermum phenolic acids made in the preparation method can directly kill chorionic villus cells, obviously enhances contractility of ingravidation uterus muscles, improves complete abortion rates of mifepristone, and is effective adjuvant resistant to early pregnancy.