In order to meet the needs of carrying out the transverse force test in wind tunnel, according to the measurement principle of the angle of side-slip and using the trigonometric function relation, by analyses of the angle measurement methods error sources and combined with the practical structure of the FL-32 wind tunnel, a new angle measurement method is set up for the double-rotate-axis. The new measurement method can obviously improve the measuring accuracy of the angle of side-slip, and also the reliability and applicability of the double-rotate-axis is improved by optimizing the local structure. The wind tunnel test results show that the double-rotate-axis can meet the requirements of the wind tunnel transverse force test in the FL-32 wind tunnel.