The effects of polycarboxylate type water reducer(PC) on working performance, strength, water absorption and corrosion rate of model gypsum were presented. The mechanism was analyzed by measurement of electric conductivity, the temperature rise of hydration, SEM and BET. The result shows that PC content of 030%(by mass) had a high reduction rate of 187%(by mass) to improve the workability of gypsum which made the working time extended for 4min and the setting time lengthened slightly. The strength and corrosion properties of gypsum were significantly increased. Flexural strength and compressive strength were improved by 22% and 57% at 0. 30% of PC content, and the corrosion rate decreased from -0. 93% to -0. 15%. Water absorption rate decreased with the increase of PC content. The mechanisms show that the adsorption on the surface of gypsum is the base for PC to the function. The hydration process of gypsum delayed to some extent. The dimension of dehydrate crystal is fined. The amount of pore in gypsum is lessened and the sizes become smaller. The corrosion was remarkably diminished.