In this study, in three models of CRASH - negative skewness of NSKEW stock returns - DUVOL bottom-up fluctuation stock risk has been calculated. The statistical sample of this research includes 96 companies listed on the Tehran Stock Exchange studied in the period 2014 to 2016. The ordinary least squares regression model was used using the combined data method to test the hypotheses. The results of the first hypothesis indicate that in the CRASH model, at the level of 97% confidence of the auditor-customer relationship, there was no significant relationship with the risk of the future stock falling in companies listed on the Tehran Stock Exchange. However, at the level of 92% confidence, the auditor-customer relationship has a significant relationship with the risk of future shares falling in companies listed on the Tehran Stock Exchange. In the NSKEW model, at a confidence level of 97% and 92%, the auditor-customer relationship has no significant relationship with the risk of the future stock falls in companies listed on the Tehran Stock Exchange. In the DUVOL model, at the level of 97% and 92% confidence, the auditor-customer relationship has a significant relationship with the risk of future stock fall in companies listed on the Tehran Stock Exchange. Therefore, the auditor-customer relationship with the risk of the future stock falling in different models in companies listed on the Tehran Stock Exchange is significantly different. The results of the second hypothesis indicated that in the CRASH and NSKEW models, with the increase of the auditor-customer relationship, the risk of future shares falling in the companies listed on the Tehran Stock Exchange decreases. But in the DUVOL model, with the increase of the auditor-customer relationship, the risk of future shares falling in the companies listed on the Tehran Stock Exchange does not decrease. Therefore, with the increase of auditor-customer relations, the risk of the future stock falling in different models in companies listed on the Tehran Stock Exchange does not decrease.
