The moving particle semiimplicit (MPS) meshfree particle method was used to analyze the churning loss of gear in the transmission system. The single helical gear was analyzed with such variables as gear width, immersion depth, and rotation speed. The results show rotation speed has the most significant influence on churning loss followed by immersion depth and gear width. Then the churning loss calculation formula was proposed by using the analysis results. The MPS feasibility and accuracy in the domain of churning loss analysis were validated by experiments. This paper provides a new method for gear churning loss research.