For economical and convenient construction of road pavement, the prefabricated road base is used in pavement engineering as a new construction technique. The same as the other prefabricated structure, the joints of prefabricated road base blocks need a caulking material to fulfill and connect, and cement mortar is selected because of its superb properties in mechanics and workability. Aimed to evaluate the cement mortar with different additives, such as redispersion emulsoid powder and defoamer to meet the needs of prefabricated road base, three experimental groups of cement mortar are compared with the control group through mechanical properties tests, durability tests, and fatigue tests in this paper. By analyzing the results of these laboratory experimental tests, it can be found that the addition of redispersion emulsoid powder in the cement mortar can improve the deformability and the ability of frost resistance, and the addition of defoamer can improve the mechanical properties but decrease the frost resistance. And the cement mortar with redispersion emulsoid powder and defoamer obtains an excellent fatigue performance.