In recent years, two opposition theories, reciprocity theory and the level-of-aspiration theory (LOA) have been developed in the negotiation process, which considers the negotiation parties to be influenced by the complex nature of human behavior. The role of talks between auditors and clients is crucial in improving financial statements quality and resolving disputes. Accordingly, they negotiate conflicts management, and adopt different strategies in order to resolve conflicts and reach an agreement. One of these important strategies is the concession strategy, which influences the various factors on its adoption by the auditor. Accordingly, the purpose of this study is to identification and ranking the factors influencing the adoption of the concession strategy by the auditor in negotiations with the client. For this purpose, in the first step, 11 factors (4 dimensions) were investigated by studying the theoretical and experimental litrature of the research. Using the delphi methodology and during the year 2018, the 21 experts (CPA) were screened and validated by effective factors. In addition, three other factors were determined by experts suggestion. In the second step, 14 sieve and confirmation factors in the previous step were ranked by using paired t-test and fuzzy hierarchical analysis method. The findings of the study showed that the behavioral characteristics (experience and techniques of negotiation, previous negotiations and past relationships with the client, the style of communication, method and negotiation, flexibility and pressure of the client and time behavior), corporate governance (audit committee and audit fees), rules and regulations and professional conduct (audit opinion, independence of auditors, power and bargaining, competition in the audit and compulsory audit market of auditors) and auditors' gender are influenced by the auditor's adoption of the rating strategy. Research findings are in line with The level-of-Aspiration Theory (LOA).