The article is based on the data of A-share heavy asset enterprises in Shanghai and Shenzhen from 2010 to 2022, and uses the double fixed-effect model to deeply analyze the impact mechanism of short-term loans for long-term investments on the investment efficiency of heavy asset enterprises from the perspectives of agency costs and financing constraints. The study found that short-term loans for long-term investments is significantly positively correlated with heavy asset enterprise inefficient investments, with agency costs serving as a mediator between the two, and financing constraints playing a moderating role. Short-term loans for long-term investments increase agency costs, thereby lowering the investment efficiency of heavy asset enterprises, especially exacerbating over-investment tendencies. Moreover, the impact of short-term loans for long-term investments on the investment efficiency of heavy asset enterprises is more severe as financing constraints are higher. Further research shows that：heavy asset enterprises with high ownership concentration can effectively inhibit the negative impact of short-term loans and long-term investments compared with heavy asset enterprises with low ownership concentration；The positive effect of short-term loans and long-term investments on the investment inefficiency of heavy asset enterprises varies across institutional attention groups, and the positive effect is stronger in the low institutional attention group. The conclusion of the study, provides new ideas and empirical support for heavy asset enterprises to optimise their financing structure, strengthen their risk management, and efficiently carry out their investment and financing activities, and is of some revelation to the improvement of the regulatory measures of the financing environment in the market and the optimisation of financial and credit resource allocation.