The study and exploration level is relatively low in the Qiaoergu-Qiha area of Erlian Basin. In order to prospecting and predicting sandstone type uranium mineralization，the sand body structure，scale and genesis should be studied first. In this paper，the genesis of target bed for sandstone type uranium deposits in the Upper Member of Saihan Formation was analyzed in detail by outcrop investigation，core observation，sandstone grain size analysis and sand distribution system mapping. It was found that the sand body in the Upper Member of Saihan Formation was banded and generally distributed from southwest to northeast. The sedimentary environment was river sedimentary system and the middle and lower part（Depositional cycle I and II）of the Upper Member was braided river deposit with large scale sand body and good connectivity，while the meandering stream system developed in the upper part with small scale sand body and poor connectivity. Braided river facies is the favorable sedimentary facies for sandstone type uranium mineralization in the study area. Uranium mineralization is vertically distributed in the braided river sand body in the middle and lower part（Depositional cycles I and II）of the Upper Member of Saihan Formation，and distributed in the places where the braided river turns，intersects and the transition zone from both sides of the short axis of the heart beach to the flood plain.