Shaft-hole fit is one of the most basic assembly structures for mechanical products, and the fit clearance plays a decisive role in the performance, safety, and effective operation of the product. Taking the uncertainty of the shaft-hole clearance fit in the positioning process as the research objective, based on the analysis of the factors affecting the uncertainty of the shaft-hole clearance fit in the positioning process, an information entropy model of the shaft-hole machining uncertainty is constructed to quantitatively describe the uncertainty of the shaft-hole clearance fit. Propose using the shaft-hole clearance fit uncertainty index to comprehensively characterize the uncertainty of the shaft hole clearance fit accuracy retention, and the inherent relationship-between the uncertainty index and the reliability of the accuracy of shaf-hole clearance fit is analyzed; the effectiveness and feasibility of the method are verified through examples.