With the enthalpy\|porosity method and single\|phase governed equations,considering the feature of melting and solidification processes,simulation on three-dimensional transient phase transformation processes under natural convection condition is completed.All that is based on the general code PHOENICS package.The typical gallium phase transformation problem has been used for benchmar king the numerical schemes. The caculated results have been found to be fair agreement with the experimental data, so that simulation for temperature, velocity fields and the location of solid liquid interface front during phase transformation process can be proved to be reliable.