Modular bridge construction projects face complex schedule management and optimization challenges, and traditional schedule control methods are often difficult to meet the actual needs. This paper proposes a combined design theory based on the critical path earned value method and Monte Carlo simulation method to optimize the progress of modular bridge construction. This paper takes a bridge construction project at a certain location in Village A as the research object, and introduces the critical path method on the basis of the traditional earned value method, so that the earned value method can more accurately reflect the different impacts of each critical work on the schedule. Then the mathematical characteristic solution is derived through Monte Carlo simulation, which more accurately gives the cumulative probability of completion of the modular bridge construction project and achieves the purpose of quantitative evaluation of the schedule. The critical path earned value method in this paper digs out the targeted reasons for cost deviation, and shortens the project duration by increasing the direct cost of the project several times, so that the cumulative probability of completion of the modular bridge construction project reaches 90.458%. It shows that the combination design theory in this paper is beneficial for the company to improve cost control in modular bridge construction projects.