Given the limited scope and effectiveness of monetary policy and fiscal policy， how to stimulate the vitality of private investment is an important policy issue. This paper takes the industrial chain effect of zombie firms as the starting point to discuss how trade credit and product pricing affect the investment decisions of private firms， striving to provide new theoretical and policy perspectives for stabilizing private investment. The empirical results show that downstream zombie firms will significantly reduce the investment scale of upstream private firms. In terms of trade credit channel， when upstream firms suffer accounts receivable defaults from downstream zombie firms， their “endogenous financing” will be reduced and their financing constraints will be strengthened. In terms of product pricing channel， downstream zombie firms reduce the markup of upstream firms， thereby squeezing the marginal income of their investment and profit margins. Solving the debt payment default and downward pressure on pricing by zombie firms to private firms is an effective tool to stimulate private investment.