The criticisms connected with the traditional approach for variance analysis of conversion cost focused on using variance of volume for measuring exploitation of productive capacity, and negligence of increasing in the production, also using working hours, and the time of machines working as a basis for counting carrying rates of conversion costs, and counting the variance. When variance analysis was not restricted in determined group of changes, and the changes which are used in the analysis can change according to what develops and appears of situations and needs, so variance analysis in its present form does not provide suitable information about the competitive attitude of economic unit from costing side. Therefore, it is necessary to improve and modify the traditional method of variance analysis of conversion cost under needs and strategies of modern industrial systems, to fit the variance analysis in a way that treats the criticisms which were directed to this style, the role of standard costs system in support of control systems and performance correction, and achievement the strategy of continuous improvement. The research tries to study the criticisms which were directed to the traditional method of variance analysis of conversion cost, then to apply the modern method of variance analysis of conversion cost, and which suits with requirements of modern industrial environment, in company of Banias Refinery, and the researcher reaches to series of results, the most important of those are: The changes which happened in modern industrial environment affected the traditional analysis of variance of conversion cost; The traditional analysis of variance of conversion cost doesn't encourage the continuous improvement; The traditional analysis of variance of conversion cost doesn't refer to movements of stock in its different types; and The total variance of conversion cost in company of Banias Refinery is (-399845730) , that is actual conversion cost bigger than standard conversion cost to the actual production.