Abstract: On the basis of the simplification of Planck function in a low temperature range,this paper modifies the practical split-window algorithm proposed by Mao et al.and presents a method for retrieving the snow surface temperature(Ts) based on MODIS data in middle-latitude region.The application of this method in Qinhai Lake region reveals that it is feasible for the retrieval of Ts.The result of correlation analysis indicates that there is obvious negative relationship between Ts and altitude.By analyzing three typical areas in which land cover is relative homogenous,this paper discusses the relationship between Ts and normalized difference snow index(NDSI) and then presents a new concept named "NDSI-Ts space".