Abstract: In LNG systems, LNG storage tank facilities make up a large proportion of investment. In order to save investments, LNG storage tank can be optimized based on the relationship between pressure and evaporation rate. Compared with single-capacity tank of LNG, full-capacity tank of LNG provides more economic and safety advantages. Structure of insulation system of full-capacity LNG tank and its optimization principle are described. The author considers that it is necessary to change tank pressure and store gas under high-pressure by adjusting the thickness of insulating layer instead of boosting system of tank, and recondensate the BOG with compressor to recycling LNG under safe running of tank. So an optimized mathematical model for LNG tank is built and VC++ language is used to write a calculation program for the solution. Case analysis shows that the model is available to reasonable optimization and use for LNG system.