Abstract: After the pretreatment of melting down in sodium peroxide, extracting with hot water, precipitating with beryllium salt, and eliminating the influence of calcium and magnesium with EDTA, tin in the samples were determined by polarography in a hydrochloric acid-ammonium chloride solution. This method improved and simplified the method described in the National Standards. The melting method, testing temperature and the interferential elements in the determination of tin in geological samples by polarography were discussed, and the working conditions of instrument were optimized.The detection limit of tin in this method was 10.0 μg/g. The measured values and standard values of the method were in reasonable agreement with analyzing the standard reference materials. The results from different instruments and methods were consistent.The method is highly accurate, with the precision(RSD,n=12)<2%. It has high efficiency, the measuring results were accurate and reliable. The method has been applied to the analysis of a large number of geological samples.