For the vertical and horizontal dual 5-axis system of a new turning-milling compound machining center, the dedicated post processor for 5-axis is developed by C++ programming language, B-axis pendulum angle error measurement technology and nonlinear error compensation algorithm are studied; and also analyzed and verified in actual processing; Researches show that: the dual 5-axis post processor works correctly and efficiently, better processing accuracy than 0.05mm can be obtained by nonlinear interpolation compensation for B-axis pendulum angle for 3 times, which meets the demand of crafts machining.