The cold-formed steel member can arrange the most suitable shape of section according to the material needed. It can increase the load capacity and decrease the weight index when it is used for power transmission towers. The effect of cold-forming procedures to cold-formed steel members is different according to the thickness of steel plate or strip. The design method of cold-formed steel members considering the strength in Chinese code of cold-formed thin-wall steel is proposed when the thickness is less than or equals 6mm. In order to study the effect of cold-forming procedures on the strength of steel, the mechanical property tests are developed on flat plates, adjacent angles and angles, which are cut from cold-formed thick-wall lipped angles. According results of test, advices on improving the formula is proposed, which is used to design the member(t≤6mm) in China, and the design method of cold-formed thick-wall steel members considering their strength is proposed. These will provides technical supports that the cold-formed steel member can be used on power transmission tower broadly.