Abstract: In the determination of residual pesticides in onion,garlic and chives by GC-MS,the sample was treated with phosphoric acid or with microwave before crushing,to make the allinase inactive and to eliminate the matrix interference.As shown by the experimental results,the treatment either with phosphoric acid or by heating with microwave,the interference of high background values was effectively eliminated.By treating with phosphoric acid,recoveries of more than 90% of the 75 kinds of pesticides tested,were found in the range of 70% to 120%.