Combining theoretical analysis and empirical research, this paper constructs a theoretical framework for the threshold model on the basis of a review and classification of relevant documents, for instance the empirical study on the existence of monetary policy bank credit channels and the study on the micro transmission mechanism of China's monetary policy credit channels. Based on the actual situation in China and the current state of China's enterprise financing policies, financing constraints, and investment efficiency, this article selects the data of listed companies in China from 2015 to 2021, chooses the balanced panel data as the research object, and obtains 8745 samples from 11624 samples via the balanced panel processing. The empirical analysis of descriptive analysis and regression analysis indicates that when the national monetary policy is maintained at a permissive level, the efficiency of SME joint investment portfolios may be considerably enhanced. In the future, the main monetary policy objectives when China is implemented should be scientifically formulated according to the main characteristics of the behaviors of microeconomic subjects in different industries as much as possible, and a differential monetary policy more suitable for "targeted" development should be adopted to maximize the effect of economic policy, so as to effectively promote the rapid and healthy growth and progress of small and medium-sized enterprises and the stable, sustainable and coordinated development of regional economic development.