This paper is a. summarization of experience gained in the analysis of samples from the whole island undertaken jointly by five laboratories in the transprovincial contract project for 1:200,000 regional geochemical prospec ting of Hainan Island organized in 1986 by Ministry of Geology and Mineral Resources. It deals systematically with the understanding of such quality para meters as detection proportion, monitoring of standard samples of Grade I and Grade II, internal check and cipher sample check as well as the ex perience acquired in quality monitoring.In the aspect of how to guarantee the analytical quality, these understand ing and experience are probably of referential value to geologic laboratori es of various provinces which are performing analysis of 1:200,000 regional geochemical samples, geophysical parties which are undertaking the task of piecing together and compiling maps and, especially, laboratories which are jointly charged with the analysis of samples from the Hainan province.