Abstract: The discrete phase data should be fitted to calculate the reticle position of computer generated holograms (CGHs) for off-axis aspheric surfaces. The basis functions of uniform B-spline and non-uniform B-spline were deduced in detail, and the corresponding fitting methods were introduced. With an off-axis paraboloid as an example, its discrete phase data was got and fitted by uniform B-spline and non-uniform B-spline. The results show that all the data points are on the fitting surface and the fitting accuracy can meet the requirement. Meanwhile, the expression of the phase function is very simple (the highest order is only three). Moreover, the sample points can be optimized to control the amount of calculation.