Abstract: Interior auditing is regarded one of the significant tasks in economical sectors due to the increasing the role auditing plays in estimating the interior inspection, endorsing the governing and participating in managing the risks in order to achieve an additional credit for the economical sector. This increasing role popped out because of the bulkiness of the economical sectors, their ramification, vigorous competition and the international crisis in the past decade. Interior auditing can protect sector’s rootstocks and, therefore, administration paid attention to interior auditing particularly in the presence of solid criteria which consolidates and endorses the applied procedures in those sectors. This research attempts to study the means for promoting the effectiveness of interior audit by applying the international auditing standard 500 for auditing evidence. The principal hypothesis was testing the possibility of promoting the effectiveness of interior audit by applying the international standard 500 for auditing evidence. There are four other minor hypotheses. In order to test these hypotheses, the factory for ready-tailored clothes in Najaf was chosen as a sample. Inspecting section, interior auditing and risks in certain items were investigated in accordance to auditing evidence and role of optimizing interior auditing in evaluating trust degree in statistics. Finally, a set of conclusions and recommendations were put forward.