Abstract: A portal frame structure is more sensitive to wind loads than the common low-rise buildings, because of its light weight, great flexibility, and lower damping characters. At present, one of the best methods to analyze the background effective static load of the common low-rise building is Load-Response-Correlation method (LRC method). However, it is difficult to be directly applied to engineering practice by the insufficient in its complicated computation, complex response to location and type. This paper used a simplified LRC method- Load-Lift-Correlation method (LLC method) to solve the background effective static load of the light-weight steel structure. Combining with a specific project example，we used the finite element software to establish different roof span portal frame structure models, selected the junction of the purline and roof as the research node of reflecting vertical wind-induced vibration response, solved the background effective static load of the light-weight steel structure in the maximum lift, and contrasted with the load which analyzed by the load code for the design of building structures. Research shows that, the effect of vertical wind-induced vibration to the portal frame structure cannot be ignored and should be taken into account in the design.