A low adsorption clay-resistant polycarboxylate superplasticizer (KN-PC) was synthesized using acrylic acid and isopentenol polyoxyethylene ether as the main reaction materials. The structural characterization and clay-resistant mechanism of the KN-PC were explored using Fourier transform infrared spectroscopy and X-ray diffraction, and the effect of the KN-PC on the performance of composite paste with various montmorillonite (MMT) contents was analyzed. Compared with ordinary polycarboxylate superplasticizer (PC), the KN-PC has a low sensitivity to the MMT. By the action of the MMT, the adsorption dosage of the KN-PC on the MMT is much smaller than that of the PC.