The use of hydrodynamic transmission with lock-up clutch for a Chinese city bus leads to good fuel economy and ease of operation. Many examples have shown that the microprocessor-based control system used in a vehicle powertrain has the advantage with high control speed over a manual one, but most of the time, its control qualities are poor, especially when outside conditions change. In this paper, a synthetic control method for hydrodynamic transmission for a Chinese city bus is proposed with respect to control qualities of lock-up control. The lock-up control process is divided into two steps, i.e., ‘estimate’ step and ‘fine’ step, so we can apply different control schedules to realize different control demands and get better control qualities. At ‘estimate’ step, we answer the question about when the lock-up clutch engages and releases to get high fuel economy and driveability, and at ‘fine’ control step, we solve the problem of how to control the lock-up clutch engagement transition to eliminate shudder and not shorten the lifespan of the clutch. Microprocessor-based electro-hydraulic controller is used here, and software and hardware are described. Simulation and road test show that the use of this control system for the hydrodynamic transmission with lock-up clutch of a Chinese city bus has improved control qualities of the vehicle.