Based on the research samples of China's A-share state-owned listed companies from 2008 to 2017, this paper examines the relationship between mixed ownership reform, competitive strategy and cost stickiness of SOEs. The research finds that the SOEs with different strategic forms will show different cost behaviors. Compared with the cost leading strategy, SOEs implementing the differential strategy have higher cost stickiness; At the same time, it is found that the mixed ownership reform of SOEs can effectively restrain the stickiness of expenses, and its inhibiting effect is more obvious in the differential strategy; The analysis of the intermediary mechanism shows that compared with the state-owned enterprises implementing the cost leading strategy, the SOEs implementing the differential strategy will strengthen the cost stickiness by aggravating the agency problem of the management. However, the mixed ownership reform of SOEs will reduce the agency problem of management, thus inhibiting the stickiness of enterprise expenses.