The purpose of this study is economic analysis of heating and cooling systems that are using gas, geothermal energy through life cycle cost analysis. The adapted research method selected the office building in Seoul region. The building is 15 stories and have total floor area of $270,000m^2$. And the capacity of heating and cooling system applied in new building is 700RT to 750RT as a scale of heating and cooling system that can provide same capacity. The Adapted LCC Analysis period on 40 years. Comparing and analyzing life cycle cost about each heating and cooling system in cases, economical evaluation is estimated. The results are as follows: 1) The total life cycle cost of gas heating and cooling system is approximately 7,979million won, the total life cycle cost of geothermal heating and cooling system is approximately 8,073million won. 2) The cost of the geothermal heating and cooling system is higher than gas heating and cooling system about 1.18%. Thus, optimal plan is the gas heating and cooling system.