This research has investigated the effect of market concentration, market share distance and auditor leadership on audit quality in the capital market (Tehran Stock Exchange).
 In this research, the issue of competition in the audit market and its effects on audit quality was investigated. Based on economic theory, three competitive criteria of the auditor's power in the market were defined and studied: concentration, market share and leadership in the market.
 advanced research, by testing the efficiency of scientific topics and developing applied knowledge about the correlation between variables in order to adapt to the previous theoretical literature, from the aspect of the applied goal, from the aspect of the quantitative research process, from the aspect of the method of collecting and analyzing information. Descriptive correlation and logically, it is an inductive research. In order to test the hypotheses in the research models, the information of the companies admitted to the Tehran Stock Exchange during the period 2012 to 2020 was used for the main purpose of the research. The information of 143 companies was collected, processed and analyzed by appropriate descriptive statistics methods and inferential statistical methods to identify the type of composite data and using R statistical software.
 The results showed that there is a significant relationship between auditor market concentration and audit quality. There is a significant relationship between industry market share and audit quality. There is no significant relationship between industry leadership in the market and audit quality.