Abstract: The qualitative analysis method of methamidophos(MAP) was approached. The developers of MAP in Thin Layer Chromatography(TLC) was decided in the experiments, and the chromatogram condition of MAP in Gas Chromatography-Mass Spectrometry(GC-MS) was studied. It is shown that polar solvents must be concluded in the developers such as ethanol, methanol, acetic acid and the developers which fit MAP are chloroform-ethanol, chloroform-methanol-cyclohexane and so on. MAP can be determined accurately by GC-MS and its retention time was 3.48 min, and the spectrum of MAP was consistent with the standard data.