Taking the Second Bridge of Yueyang Dongting Lake as engineering background，wind tunnel test method was used to study the three-component force coefficients in horizontal direction and the drag coefficients along the bridge axis of a plate-truss composite stiffening girder（PTCSG） in service and construction stages under different attacks and yaw angles，respectively. The influence of compensation model with different length was also investigated. The expressions of longitudinal drag coefficients of the PTCSG in service and construction stage with yaw angles were fitted，respectively，based on the experimental data. The results show that，when the wind tunnel tests of longitudinal drag coefficients of PTCSG under skew wind are carried out，the accuracy requirements can be basically satisfied when the length of the compensation section model is about 30% of that of the force measurement model. The longitudinal drag coefficients of PTCSG increase first and then decrease with the increase of yaw angles，which reach the maximum at about 50° ~ 55° yaw angles. The drag coefficients in horizontal direction of PTCSG increase first and then decrease with the increasing yaw angles，reaching the maximum when yaw angle is about 5° ~ 10°，and the value is about 1.05 times the drag coefficient with 0° yaw angle.