Unlike previous studies focusing on mixed-ownership reforms, mainly privatisation of state-owned enterprises, this study discusses the impact of partial nationalization and the appointment of D&Os on innovation investment and quality, measured in two dimensions: the heterogeneous shareholder governance effect and the shareholder resource acquisition effect. We find that the introduction of state-owned capital helps to promote the R&D investment and innovation quality of mixed-ownership private companies, and the introduction of state-owned capital and the appointment of D&Os have a more significant effect on the innovation investment and innovation quality of mixed-ownership private companies. The results of mechanism tests show that the impact of state capital introduction on R&D investment and strategic innovations is mainly through policy resources accesses and suppression of the tunnelling effect of non-state controlling shareholders.This paper verifies the adaptability of the shareholder resource acquisition effect and the heterogeneous shareholder governance effect in Chinese listed companies from the perspective of state-owned capital participation and the appointment of D&Os to promote the technological innovation of mixed-ownership private companies, and, at the same time, enriches the relevant literature on the economic consequences of the mixed-ownership reform from the perspective of the dimension of state-owned capital participation on the technological innovation of private companies.