The reform of the registration system of the science and technology innovation board has triggered the change of the behavior of the IPO enterprises to “Window Dressing” the statements in order to meet the listing requirements, from the “Window Dressing” of the earnings under the approval system to the “Window Dressing” of the research and development of the science and technology innovation ability under the registration system. This paper takes the listed companies on the science and technology innovation board from 2019 to 2023 as research objects. Based on the “assurance effect hypothesis” and “conflict of interest hypothesis”, this paper explores the governance effect of the proportion of brokers’ follow-up investment on the science and technology innovation board. The study found that the follow-up investment proportion of securities firms in the science and technology innovation board can effectively inhibit the level of pre-IPO R&D “Window Dressing”, which supports the “assurance effect hypothesis”. The mechanism test shows that the proportion of brokers’ follow-up investment mainly plays a role through two paths: the external market mechanism of new stock inquiry price differences and the internal governance mechanism of management compensation incentives. Heterogeneity analysis shows that among the three groups of samples with low IPO review inquiry intensity, low transparency of enterprise information disclosure and high concentration of management power, the governance effect of brokers’ follow-up investment is more significant. The test of economic consequences further finds that brokerage follow-up investment helps to reduce the probability of post-IPO trading below the offering price and the risk of stock price crash. This study provides important theoretical enlightenment for improving the design of the supporting system for the reform of the registration system, promoting the reform of the registration system and improving the quality of listed companies.