Through empirical analysis, this paper clarifies the micro-mechanism of financial friction between small and micro enterprises and large enterprises, and constructs an NK-DSGE model with heterogeneous credit constraints of enterprises. On this basis, the optimal extended Taylor rule is explored by the welfare loss analysis method, and the transmission path of the optimal policy rule is analyzed by impulse response simulation. The results show that: First, the loan financing of small and micro enterprises is very significantly affected by the price of real estate collateral, but for large enterprises, the impact on housing prices has not caused significant changes in the amount of loans. Second, the optimal extension Taylor rule that incorporates factors of loan volume and real estate price fluctuations can reduce social welfare losses, and the Taylor rule that directly targets loan volume has a more obvious effect on stabilizing credit fluctuations. Third, the optimally scalable Taylor rule that targets loan volume can reduce social welfare losses by reducing credit volatility and curbing corporate heterogeneity in loan constraint distortions.