The paper is devoted to the study of onedimensional self-similar problem of heat interaction between frozen saturated soil and atmospheric precipitates. The investigation of precipitations influence on the process of the soils freezing and the frozen soils thawing is of a great importance both for the north regions with permafrost and for agriculture in the South Siberia. The mathematical model for the phase change in frozen saturated soil under the action of a rain is formulated. The selfsimilar case is considered and the corresponding solutions are constructed. The conditions of the frozen soil thawing, the rain water freezing and of a stationary sate are studied. The particular feature of the given statement of a problem is the possibility for the free boundary to move as dawnward (process of the frozen soil thawing), so upwards (process of the rain water freezing) and also to keep the stationary position when precipitations and frozen soil are in the heat equilibrium state. This peculiarity distinguishes our statement of a problem from the well-studied self-similar solutions for different phase-change problems where the interface has the form of s(t)=β√t with the positive parameter β.