The cutter runout effect has significant influence on the shape of cutter swept surface and the machining surface quality. Hence,it is necessary to integrate the cutter runout effect in cutter swept surface modeling,geometric error prediction and tool path optimization for five-axis flank machining. In this paper,an envelope surface model considering cutter runout effect is first established,and geometric errors induced by runout effect are derived based on the relative motion analysis between the cutter and part in machining. In the model,the cutter runout is defined by four parameters,including inclination angle,location angle,offset value and the length of cutter axis. Then the runout parameters are integrated into the rotation surface of each cutting edge that is used to form the final cutter envelope surface for the five-axis machining process. Thus,the final resulting geometric errors of the machined surface induced by cutter runout can be obtained through computing the deviations from the nominal cutter swept surface. To reduce these errors,an iterative least square method is used to optimize the tool paths for five-axis flank machining. Finally,a validation example is given for a specific ruled surface. Results show the effectiveness and feasibility of the analytical model of geometric errors induced by cutter runout,and also show that the geometric errors can be reduced significantly using the proposed tool path planning method. The cutter runout effect has significant influence on the shape of cutter swept surface and the machining surface quality. Therefore, it is necessary to integrate the cutter runout effect in cutter swept surface modeling, geometric error prediction and tool path optimization for five-axis flank machining . In this paper, an envelope surface model considering cutter runout effect is first established, and geometric errors induced by runout effect are derived based on the relative motion analysis between the cutter and part in machining. In the model, the cutter runout is defined by four parameters, including inclination angle, location angle, offset value and the length of cutter axis. Then the runout parameters are integrated into the rotation surface of each cutting edge that is used to form the final cutter envelope surface for the five-axis machining process Thus, the final resulting geometric errors of the machined surface induced by cutter runout can be obtained through computing the deviation To reduce these errors, an iterative least square method is used to optimize the tool path for five-axis flank machining. Finally, a validation example is given for a specific ruled surface. feasibility of the analytical model of geometric errors induced by cutter runout, and also show that the geometric errors can be reduced significantly using the proposed tool path planning method.