Abstract: Being the most popular structure for greenhouses with rigid cladding material, Venlo greenhouse has become the first choice for greenhouse covered by glass or PC sheets in China. With the help of greenhouse structural software, the load effects on the side posts and mid-posts in seven different span greenhouses are calculated under six different load combinations by the method of structural finite element analysis. The changing regulation of internal forces born on the posts is deduced from above calculation. The greenhouse structural safety, design level can be improved and the steel amount in Venlo greenhouses can be decreased with the application of the analyzing results in greenhouse post arrangement, section selection, structure-joint design.