In phase unwrapping,how to control residuals and cut lines is the key to unwrap ill state wrapped phase map successfully.In this paper,we provide new concepts in phase unwrapping field.Firstly,we have classified residuals in three types,singular residuals,normal residuals and virtual residuals.And secondly,we have analyzed some differences between cut line and curved line.And,we propose an enhanced Goldstein algorithm to connect the different residuals.