The participation of migrant workers in medical insurance of urban workers is a formal institutional arrangement. However, in reality, the insurance participation rate of migrant workers is low and the medical insurance taken by the migrant workers is not sufficient, which seriously hinders the process of the citizenization of migrant workers. The main reason lies in the unbalanced supply and demand of the current system. With the continuous advancement of the citizenization process, the rural migrant workers’ demand for medical insurance has changed. However, our research found that the supply of medical insurance system for migrant workers is seriously inadequate, the system and the institutional environment are disconnected, the internal contradictions of the system are increasing, and a large amount of potential profits are accumulated under the current system. Potential profit is the motive force to promote institutional innovation and promote the reform of current system to strike a balance.