Abstract: The key to guarantee accurate analysis result was the pretreatment of soil sample when we determined the mercury in soil by atomic fluorescence spectrometry.Pass through some experiments of different method or different condition,we could make sure that the procedure of digestion and decomposition in high pressure by HNO₃-H₂O₂ was desirable.The result of analysing standard sample and unknown sample showed that accuracy and precision all meet the needs and this method is handy and speedy,it is worth to popularize.