The product quality will be affected by various stations during the multi-stations manufacturing. Various stations will have a mutual effect. The traditional process statistical control method can not find out the root of problems in a timely manner after errors in the products. This article has raised the concept of virtual stations on the basis of variation transferring model and then accurately find out the malfunction stations through assumption inspection. Finally, this article has taken the processing process of steering knuckle as an example to verify the raised theory.