End cracking in one side automatic welding is said to be a kind of solidification cracking. Though many analyses and experiments have been done to know expansion of root gap near the end of the plate, there is no attempt to evaluate the deformation behavier of weld metal during solidification in one side welding. In order to develop the higher welding technology, the authors are aiming to establish a criterion for occurrence of end cracking by using deformation curve (1) during solidification and ductility curve (2) in high temperature range as shown in Fig.1. In this report, authors have firstly analyzed deformation behavier during solidification in one side welding of fully large plates by modification of analytical solution using finite element method. Secondly, effects of plate width, weld length, and welding conditions on deformation behavier during solidification have been investigated. Thirdly, validity of analysis method using in this report are examined by comparing the calculated transient deformation behavier to the experimental one. Finally, authors have proposed the methods to estimate length and position of end cracking in one side welding.