Abstract: As a strengthening mechanism of family control,the excess control of family board seats will give the controlling family a strong incentive to carry out related party transactions,which will affect the stock price crash risk. The samples of family firms listed in Shanghai and Shenzhen A shares are manually identified from the sub-database of the private listed companies in CSMAR database,and the key data such as the proportion of family shareholding and the number of family directors are collected manually. Other data come from CSMAR database and RESSET database.The sample period is from December 31,2008 to December 31,2017. The degree of excess control of family board seats (ECFBS) is measured by the difference between the proportion of board seats controlled by the family and the proportion of shares held by the family. The related party transaction behavior variables are measured by Tunnel_dum and Tunnel_asset. The stock price crash risk variables are measured by CrashRisk,including two indicators of NCSKEW and DUVOL. Based on the perspective of related party transactions,the relationship between the degree of excess control of family board seats and stock price crash risk is examined. The results show that the degree of excess control of family board seats is positively related to the stock price crash risk and the related party transaction behaviorof the controlling family. The related transaction behavior of the controlling family has a significant positive effect on the stock price crash risk,and this effect is more obvious in companies with higher degree of excess control of family board seats.Further analysis shows that with a lower proportion of institutional shareholding,a combination of two positions and a smaller board size,the degree of excess control of family board seats has a stronger positive correlation with the stock price crash risk and the related party transactionbehavior of the controlling family; the related party transactionbehavior of the controlling family have a more significant positive impact on the stock price crash risk,and its interaction relationship with the degree of excess control of family board seats has a more significant positive impact on the stock price crash risk.Finally,after controlling potential endogenous problems and conducting a series of robustness tests,the conclusion is still valid.

Key words: family firms, excess control of family board seats, stock price crash risk, related party transactions