The samples were prepared with four kinds of initial moisture content, which were collected in beach area of Tianjin. Unconfined compressive strength(UCS) test and pore size analysis were carried out on the samples under different times of freeze thaw cycles. The UCS evolution process and pore size distribution curves were measured. The results show that the UCS of samples reduces while freeze thaw cycles increase, and the decrease is significant under the initial 13 cycles. Meanwhile, the higher the initial moisture content of samples, the larger the strength loss ratio under the same freeze thaw cycles. The pore size distribution curves of samples are determined by initial moisture content and freeze thawing cycles. The pore size distribution areas change from microscopic to macroscopic range with increasing initial moisture content. When the treated soils are at low saturated degree state, pores would shrink and the cracks appear due to freeze thaw cycles. However, at high saturated degree stage, the structure of soils would become porous under the effect. Overall, the micro pore structure is damaged apparently due to freeze thaw effect, and ultimately results in gradual decrease of macro strength. Hence, it is necessary to pay attention to the long term strength of the cement improved soft clay, and keep suitable moisture content during filling time.