The invention discloses a method and system for utility boiler combustion subspace modeling and multi-objective optimization, belongs to the field of utility boiler optimization operation, and particularly relates to a method and system for setting up of a high-precision combustion model and solution of multi-objective optimization. The method includes the following steps of determining input variables of a combustion optimization model, determining the variable to be optimized from all the input variables, dividing a load into a plurality of sectors with the neighborhoods overlapped, setting up a combustion subspace ANFIS model for each sector in an off-line mode, collecting data in real time, conducting partial subspace model modification in an on-line mode, conducting on-line multi-objective optimization by taking the constraint of a unit load into consideration, taking maximizing the boiler efficiency and minimizing the nitrogen oxide emission as targets, and utilizing a mature global optimization algorithm and on the basis of comprehensive cost minimization, and separating and implementing the optimization result. The method and the system are suitable for combustion optimized operation of a coal powder utility boiler and have the advantages of being high in modeling accuracy and high in optimization speed.