In pressure vessels design, WRC107 provides a typical method of local stress analysis to supports and attachments. But influence of the rigidity of attachments on calculation is not considered. For fatigue analysis of round hollow attachment on cylindrical shell, equivalent stresses calculated by WRC107 were compared with those by finite element method. Three attachment thickness configurations, that half, equal, double of the shell thickness were tested. Results show that, in key point Au defined by WRC107 equivalent stress decreases while attachment rigidity increases, and in key point Cu, equivalent stress increases while attachment rigidity increases. When the thickness of attachment equals to that of shell, equivalent stress of WRC107 in Cu comes closest to FEM.