In machining complex parts with high speed milling, small contour error (CE) and high surface quality are usually two major concerns. Many papers have focused on reducing CE by online contouring adaptation in the presence of disturbances and/or uncertain nonlinearities. Besides, calibration methods on pre-machining process such as smoothing the setpoints with optimized feedrate are also preferred. In contrast, less efforts have been done to analyze the relationship between profile geometry, control tuning or adjustment and effective CE in order to obtain CE as small as possible. To effectively deal with this challenge, an Offline Gain Adjustment (OGA) algorithm is developed in this paper. The simulated comparisons with existing fixed gain controller prove the efficiency of the proposed OGA method.