Combined with ultrasonic wave extraction, a pre-column derivatization reaction high performance liquid chromatographic ultraviolet detection procedure was developed for the determination of atrazine and simazine in soil and crop. The 4-(2-phthalimidyl) benzoyl chloride (PIB-Cl) was used as a pre-column derivatization reagent for high performance liquid chromatography (HPLC). The ultrasonic wave technique was applied to the extraction for trace atrazine and simazine in soil and crop. The clean-up and second-time concentration procedures, which was indispensable in the conventional analytical methods for soil and crop analysis because of the complexity of the samples, were replaced by derivatization reaction between PIB-Cl and analytes. The optimum absorption wavelength of 345 nm and the molar absorption coefficients of 105level for the derivatives were found.