In order to break through the current bottleneck of conveniently applying site model to BIM forward design, this paper proposes a method for lightweight site model production and model quality evaluation. The method first analyzes the data structure of the site model, and uses the LOD principle to realize the lightweight processing of the site model; then, based on the existing site model quality inspection specifications, it proposes improved quality evaluation factors, their weights and threshold intervals, and uses the quality score to test product quality. Finally, it is verified by actual engineering.