The utilization of new regional geochemical exploration methods in the forest-swamp area has widened the application range of regional geochemical data and enabled these data to be used in basic geological survey. As stream sediments in the forest-covered area have a high content of organic matter, this study chose the coarse fraction stream sediments, which could easily exclude the impact of organic matter. Exemplied by the steam sediment survey in the Da Hinggan Mountains as an example, the authors made a comparative study of two sizes of fractions, i.e., -10～60 meshes and -10～40 meshes, and compared the surveying results by Geochemical Anomaly Map and Variance Analysis. The research results show that there is no essential difference between the two sizes of fractions. 