Biomass gasification based building cooling, heating, and power (BCHP) system is an effective distributed energy system to improve the utilization of biomass resources. This paper proposes a combined methodology of optimization method and life cycle inventory (LCI) for the biomass gasification based BCHP system. The life cycle models including biomass planting, biomass collection-storage-transportation, BCHP plant construction and operation, and BCHP plant demolition and recycle, are constructed to obtain economic cost, energy consumption and CO2 emission in the whole service-life. Then, the optimization model for the biomass BCHP system including variables, objective function and solution method are presented. Finally, a biomass BCHP case in Harbin, China, is optimized under different optimization objectives, the life-cycle performances including cost, energy and CO2 emission are obtained and the grey incidence approach is employed to evaluate their comprehensive performances of the biomass BCHP schemes. The results indicate that the life-cycle cost, energy efficiency and CO2 emission of the biomass BCHP system are about 41.9 $ MWh(-1), 41% and 59.60 kg MWh(-1) respectively. The optimized biomass BCHP configuration to minimize the life-cycle cost is the best scheme to achieve comprehensive benefit including cost, energy consumption, renewable energy ratio, steel consumption, and CO2 emission. (C) 2014 Elsevier Ltd. All rights reserved.