Phase transformation and volume expansion of pore water at low temperature are the main reasons of the frost heaving damage in rock. The tensile strength of rock after freeze-thaw cycles is worthier of attention than the compressive strength. To investigate the mechanics of rock under tensile stress, this work proposed an approach based on the concepts of pore water particle and volume expansion to simulate the processes of phase transformation and frost heave of pore water at low temperature. The equation for expressing the relationship between the volume of pore water particle, temperature, and unfrozen water content was derived. Then, the new proposed approach was used to carry out the simulation of freeze-thaw cycles on water rich rock samples. The feasibility and reliability of the new proposed approach were verified by comparing the simulated results with the laboratory test results. Simulated results indicate that cracks inside the disc formed during the process of freeze-thaw cycles tend to gather near the surface. When the number of freeze-thaw cycles is small, the cracks inside the disc formed during the splitting test are mainly concentrated near the center line of the disc, while a large number of cracks will be generated far from the center line of the disc when the number of freeze-thaw cycles is large. The tensile failure rate is much higher than the shear failure rate in both the processes of freeze-thaw and Brazil splitting test.