The legal responsibility of auditors is required. Before final acceptance of the job audit, the auditor should identify and assess cognitive activities in the internal control system to be able to handle the volume required for an efficient audit rational and effective to give them. In this paper we try to quantify the components of audit risk by providing a reasonable method to determine the number of samples required for the expression of professional items, according to the internal control system understanding risk these Risk of by inherent auditors have.