Abstract: The regulatory role social trust plays in the separation of ultimate controlling shareholders’ control right and cash flow right and capital structure deviation is explored using the data of SMEs. The empirical results show that the greater the separation degree of the two rights， the greater the degree of capital structure deviation， and the comprehensive level of social trust can alleviate the adverse effect of the separation of the two rights on capital structure deviation. According to the state-owned and non-state-owned nature of ultimate controlling shareholders and the strong control mode and weak control mode， a further empirical test shows that the different ownership nature and different control modes of ultimate controlling shareholders have different effects on capital structure deviation due to the separation of the two rights， and there are certain differences in the regulatory role of social trust between the two.

Key words: social trust; separation of two rights; capital structure deviation; regulatory role; governance mechanism