Mechanical properties of cement mortars modified by hydroxyethyl methyl cellulose, ground granulated blast furnace slag and superplasticiser, including compressive strength, flexural strength, elastic modulus and tensile bond strength, were investigated. Furthermore, relationships between those properties and bulk density of fresh mortars as well as porosity of hardened mortars were also studied. The research results showed that compressive strength of cement mortars has a good relationship with bulk density of fresh mortars and porosity of hardened mortars, flexural strength has a part relation with them, but tensile bond strength has no relation with them. Superplasticiser and ground slag can enhance the compactness of mortar and reduce its porosity, which improves its compressive strength, flexural strength, elastic modulus and tensile bond strength. Hydroxyethyl methyl cellulose is able to maintain tensile bond strength but decrease compressive strength and elastic modulus. The combination of superplasticiser, ground slag and hydroxyethyl methyl cellulose may not only increase the tensile bond strength of mortar, but also made it have enough compressive strength, flexural strength and elastic modulus. Therefore, with the proper addition of hydroxyethyl methyl cellulose, the modified cement mortar can be used as bridge pavement and corresponding repair materials.