Based on the data of China’s A share listed firms from 2003 to 2021, we empirically examine the effect of common ownership on the financialization of firms and its mechanism of action. The findings suggest that common ownership exerts a collusive cohort effect and promotes the financialization of firms. Mechanism tests find that common ownership promotes corporate financialization by accelerating financialization synchronicity and exacerbating agency problems, and that macroeconomic policy uncertainty and creditor supervision weakens the collusive cohort effect of common ownership. Heterogeneity analyses find that the collusive cohort effect of common ownership is more pronounced in samples with higher same industry power or non state enterprise, and a greater tendency to allocate speculative short term financial assets while promoting the financialization of firms. This paper not only provides new evidence for the collusive cohort effect of common ownership, but also provides some theoretical reference for the government to guide the enterprises “from the virtual to the real”.