Abstract: OBJECTIVE To optimize the extraction conditions of polysaccharides from Poria cocos (Schw.).Wolf and to determine the molecular weight (Mw) and its distribution. METHODS Orthogonal test design was employed to optimize the extraction conditions of polysaccharides from Poria cocos (Schw.) Wolf. The ultrasonic time, solid-liquid ratio, extraction temperature and extraction time were respectively taken into account. The total carbohydrate content was determined by the phenol-sulfuric acid method, with glucose as the standard. The Mw and its distribution was determined by HPSEC-MALLS-RI. RESULTS The optimal extract condition of polysaccharide was as follows:the ultrasonic time was 30 min, solid-liquid ratio was 1:50, extraction temperature was 100℃ and extraction time was 4 h. The total carbohydrate content was 93.5%. Polysaccharides Mw of component A and component B from Poria cocos (Schw.) Wolf were determined to be 4.671×10⁶ (±1.003%) Da, 6.144×10⁴(±2.466%) Da, and the Mw distribution of A and B were determined to be 12.3% and 87.7%. CONCLUSION This method is simple and accurate, it can be used to determine the molecular weight and its distribution of polysaccharides.