In the current project construction in China, it is an important work to coordinate and cooperate among various project departments. In consideration of the resource balance, full attention should be paid to the connection, cooperation and information sharing among various departments. Taking the field of mechanical engineering planning and design as an example, this paper establishes a scheme and strategy system for scientific and reasonable resource allocation from the perspective of external environment to achieve the overall goal. After optimization, human resource allocation and personnel structure arrangement can be used to improve the efficiency of staff in the shortest time. Then, based on the multi-objective optimization algorithm, the resource balance model of mechanical engineering project is designed and the model is tested. The test results show that the model has small variance and low range, which shows that the model has excellent optimization effect.