Auditor^'s judgment and decision making is affected by factors such as audit environment, auditor characteristics, evidence, decision making process and audit personal characteristics. Decision making factors is important. Making a good judgment in complex, non-confidence and pressure-packed settings require a systematic process. So it needs to consider common biases and traps that they can affect professional judgment. Cognitive bias refers to the tendency of individuals to make systematic judgment errors when making decisions. Judgment errors typically result from information processing shortcuts or heuristic behaviors that are “hardwired” or embedded into human decision-making processes. Dozens of cognitive biases have been identified and catalogued by psychologists, including several that are often mentioned in everyday conversations. But some of these biases are important. In this paper, these biases are introduced and some preventing strategies are presented.