This invention provides a flexible polymer modified waterproofing cement material which can be used on a substrate or in concealed areas of construction engineering, water conservancy projects, municipal works, and its making process. The waterproofing material is made by kneading a hydraulic cement, a polymer dispersion, a water-soluble polymer or re-dispersible resin and water at a weight ratio of cement/polymer of about 100:15 to about 100:150 under conditions of about 25° C. to about 120° C., about 20 rpm to about 80 rpm until the water content of the kneaded materials reaches about 5% to about 20%. The kneaded material is mixed with a toughening polymer at a weight ratio of about 100:10 to about 100:50, then is calendered into sheets. These materials can adhere to dry or wet substrates firmly. They can be used in cold or hot and wet climate areas. After application, the waterproofing structure formed can bear retractive stress and deformation of the base or can resist outer impact.