In view of the negative effect of the clay in the concrete, two kinds of low molecular weight clay-retraining reagents, PAAS and AA-AM, were synthesized through the mechanism of free radical copolymerization, ammonium persulfate as initiator, isopropyl alcohol as chain transfer. The polymers were analyzed by fourier infrared spectroscopy (FTIR), thermogravimetric (TGA) and gel permeation chromatography (GPC). Meanwhile the polymers were characterized by the cement paste fluidity, concrete slump and expansion. The results showed that the two kinds of polymers had a certain performance on inhibiting clay which could reduce the cement paste fluidity, concrete slump and expansion losing. The concrete slump increased from 180mm to 210mm and the concrete expansion advanced from 310mm to 430mm while adding the polymer AA-AM.