Abstract: Angular distortion is a serious problem in multi-pass weld. However, research on it was very lacking. The prediction of angular distortion in thick multi-pass weld is analyzed, and the existed empirical formulas about angular distortion are summarizad. A method for angular distortion analysis was put forward. Applied the basic mechanical formulas and combined the cause of the welding distortion, a new formula for the angular distortion in multi-pass weld is deduced. Two examples about thick low carbon steel butt weld with a single V-groove and thick aluminum alloy butt weld with double V-grooves are illustrated.