By the laboratory study on the base of cement stabilized crushed rock adding water reducing agent, the physical and mechanical properties of the base were investigated. Because of the effect of reflective cracking, shrinkage was on the focus. It is showed that susceptibility of the maximum dry density to the water dosage on this base is reduced and the base can be compacted more easily. These characteristics are useful for the on site quality control. At the same time, the splitting tensile strength of the base is improved but the compressive strength fluctuates. The reason is, in the field of little water content, the compressive strength of concrete does not follow the water-cement ratio rule. The shrinkage of the base decreases by the proper dosage water reducing agent. Furthermore, it is also found that the performance of the base of cement stabilized crushed rock can be improved further by mixing water reducing agent and fly ash together.