By using UV adsorption spectrophotometer, micro electrophoresis potential analyzer, and X ray photo spectroscopy, the adsorption characteristics and surface electrochemical properties of polycarboxylate type superplasticizer（PCS）on gypsum surface and their subsequent effects on fluidity loss of fresh gypsum plaster with hydration time were studied. The results indicated that the adsorption behavior of PCS on gypsum particles follows a Langmuir isothermal adsorption model with an adsorption heat of 20.85 kJ/mol and an adsorption layer thickness of 7.5 nm. The 2p electron bonding energy of Ca element on gypsum surface takes place obvious chemical shift before and after the adsorption of PCS, which suggests that the adsorption of PCS belongs to chemical adsorption. The adsorption conformation of PCS superplasticizer is comb shaped, so it has a saturated low adsorption amount and a weak electrostatic repulsive effect, and its dispersion mainly comes from high steric hindrance effect generated by the adsorption layer. The steric hindrance is less affected by new hydration products, resulting in good dispersion stability.
