The working principle and basic structure of combined balance was introduced. Simulation program of combinatorial calculation was compiled based on LabVIEW, so as to get the pass rate of combined balance in different combination modes, different combination models and different standard deviation. The simulation results were analyzed and it was concluded that the pass rate of combined balance has something to do with combination mode, combination model and standard deviation. Then the pass rate of combined balance was improved by optimizing combinatorial principle of combined balance.