In order to control the quality of spline shaft in rolling process,an efficient measurement method for rolling performance evaluation is essential.Here,a newly developed on-machine non-contact measurement prototype based on laser displacement sensor and rotary encoder is proposed.The prototype is intended for the automated evaluation of the spline shaft rolling performance by measuring the dimensional change of tooth root,which is correlated with the surface residual stress and micro-hardness.Laser displacement sensor and rotary encoder are used to record the polar radius and polar angle of each point on measuring section.Data are displayed in a polar coordinate system and fitted in a gear.Through multipoint curvature method,the roots of spline shaft are recognized automatically.Then,the dimensional change can be calculated by fitting the radius of the tooth root circle before and after rolling.Systematic error covering offset error is also analyzed and calibrated.At last,measurement test results show that the system has advantages of simple structure,high measurement precision (radius error ＜ 0.6 μm),high measurement efficiency (measuring time ＜ 2 s) and automatic control ability,providing a new opportunity for the efficient evaluation of various spline shafts in high-precision mechanical processing.