The wind tunnel tests were carried out to obtain the variation law of the drag coefficient of suspension porcelain insulator strings and suspension composite insulator stings with different wind velocities, wind attack angles, bundle spaces. The test models are made of the actual insulator strings and have the real rough surface. Test results show that it is unreasonable to calculate the wind load of the common and composite insulator strings with a same drag coefficient in the codes. In the two types of multiple-insulator strings, the range of the wake interference angle between the windward insulator strings and the leeward insulator strings is different. The leeward insulator strings is obviously shielded by the windward insulator strings. The shielding effect of the windward insulator strings should be considered at different wind attack angles. In the multiple-insulator strings, the variation of the bundle space has an obvious influence on the drag coefficient of the leeward insulator strings. The drag coefficient of the leeward insulator strings increases with the increase of the bundle distance. The influence degree of the drag coefficients of the leeward composite insulator strings caused by the variation of bundle space is greater than that of suspension porcelain insulator stings.