By using measurement techniques such as scanning electric microscope(SEM),mercury intrusion porosimetry(MIP),nitrogen adsorption porosimetry,hydration temperature test,hydration ratio test,and electric conductivity test et al,the influence of naphthalene-type(FDN) superplasticizer on the hydration process,strength, pore structure,and crystal morphology of building gypsum was investigated.The results indicate that the addition of FDN increases the strength of building gypsum significantly.When its dosage is below 1% mass ratio,the strength of building gypsum is rapidly increased as a function of superplasticizer addition.FDN superplasticizer has a minor effect on the crystal morphology of hydration products,but it could improve the pore structure of hardened gypsum paste markedly,leading to the decrease of porosity and average pore size,which is the very reason that superplasticizers reinforce building gypsum.