Rationalized clique behavior of institutional investors and standardized annual report disclosure of enterprises are the key factors affecting the overall stability of the capital market,which have far-reaching impacts on the high-quality develop-ment of the capital market.Based on the sample data of the A-share listed companies in Shenzhen and Shanghai from 2013 to 2020,this paper empirically examined the mechanism and effects of institutional investor clique on the tone manipulation of listed companies'annual reports using the fixed-effects model and the two-stage least squares method.It was found that:(1)Insti-tutional investor clique has a significant positive effect on the annual report tone manipulation,indicating that institutional inves-tor clique significantly exacerbates the degree of annual report tone manipulation,and the results of the robustness test still sup-port the conclusion;(2)The test of the impact mechanism showed that when the management pandering motivation is stronger and the institutional investor groups"vote with their feet",institutional investor clique will further exacerbate the degree of annu-al report tone manipulation;(3)The heterogeneity test showed that for firms with relatively weak regulation,management is more likely to manipulate the tone of annual reports in order to cater to institutional investor clique;(4)The impact effect test showed that,in the case of institutional investor clique,the tone of annual report manipulation significantly raises the risk of stock price collapse,thus impeding the high-quality development of the capital market.The findings of this paper will provide a diversified perspective for analyzing the influence mechanism of tone manipulation in annual reports at the theoretical level,and provide pol-icy insights for regulating institutional investor clique behaviors,enhancing corporate disclosure,and contributing to the high-quality development of the capital market at the practical level.