Abstract: A criterion program for weld reinforcement that combined critical solid fraction and Niyama criterion was developed based on solidification shrinkage and feeding theory in molten pool. It was adopted to numerically investigate the formation of weld reinforcement of 20 mm thick non-penetrated 2219 high strength aluminum alloy electron beam weld, and the results was experimentally verified. It was found that a large number of loose interspaces that formed upon solidification distributed in the upper-middle part of weld seam, which promoted the formation of reinforcement. The simulated reinforcement and volume expansion ratio errors were 11% and 23.67%, respectively. Therefore, The proposed criterion program in this paper can be used to reasonably predict the reinforcement.