Based on the policy of inquiry letters from the Shanghai and Shenzhen Stock Exchange. Taking Chinese A-share listed firms from 2013 to 2017 as our samples， this paper investigates the governance effect of inquiry letters supervision on controlling shareholders' tunneling behavior. The empirical results show that the regulatory of enquiry letters can effectively restrain the tunneling behavior of controlling shareholders. The inquiry letters are further divided into tunneling-related inquiry letters and non-tunneling-related inquiry letters， and we find that the supervision effect of inquiry letters on controlling shareholders’ tunneling is more pronounced in tunneling-related inquiry letters. From the motivation of controlling shareholders to conduct tunneling， the supervision effect of tunneling-related inquiry letters on controlling shareholders' tunneling is stronger in the companies with poor internal control. From the objective conditions of the realization of tunneling behavior， the governance effect of tunneling-related inquiry letters on controlling shareholders’ tunneling is more significant in the regions with lower legal level.