The mathematical model of non-stationary gas mixture transmission by the sea gas pipeline is suggested taking into consideration the possibility of pipeline glaciation. The algorithm of the numerical solution of a nonlinear model equation system is presented. The algorithm has been implemented in C++ in the form of program complex, which enables to calculate time changes of the temperature, density, pressure and speed of gas mixture in every section of the gas pipeline and time changes of an ice layer thickness on outer surface of the gas pipeline. As an example, the calculation of one of variant gas transmission is illustrated by the chart, which shows variations of the ice layer thickness for different sections. Refs 6. Figs 5.