Analysis of samples taken from the cracking area of the multilayered urea reactors verified the existence of stress corrosion cracking (SCC) cracks. The influence factors of SCC in multilayered urea reactors were investigated. The results show that the leak detection steam may condense in the interlayer clearances, which would cause alkaline medium concentration at the heavy weld. It was the initiation and propagation of micro-cracks under alkaline environment and local high stress concentrations that lead to the SCC of heavy girth weld urea of the multilayered reactors. The results can give beneficial directions to avoid SCC of layers and catastrophic ruptures of multilayered urea reactors.