Abstract: Four kinds of polycarboxylic high performance water reducer were modified by chain extender, and the best modification technology was optimized. The results show that the modified polycarboxylic high performance water reducer A only plays release effect on the dispersiveness of cement, while the modified polycarboxylic high performance water reducer B, C and D can greatly improve the dispersiveness of the cement, especially to the water reducer with poor slump performance. Furthermore, the influence of the modified water reducer on rheological properties of concrete has the same rule as that of the modified water reducer on the fluidity of cement paste. In addition, gas content, compressive strength, permeability and appearance quality of the concrete are obviously improved and the cost is also reduced. Finally, the modification mechanism of chain extender is analyzed from the point of the molecular chain structure.