Abstract: Objective Transverse cracks often occurred in the welding of high strength steel thick plates for deep-water jacket. The aim was to analyze influence of welding environmental factors on transverse cracks in the welding of high-strength steel thick plates. Methods G-BOP test was used to test sensitivity of transverse cracks under typical temperature and humidity combination conditions. Effects of diffusion hydrogen content, microstructure of weld and restraint stress on crack initiation and propagation behavior were analyzed. Results The results showed that in the environment with temperature of 10 ℃ and humidity of 90% (low temperature and high humidity), content of diffusible hydrogen in welds reached 9.9 mL/100 g, with a cracking rate of 66.7% and the highest sensitivity to transverse cracks. In the environment with temperature of 38 ℃ and a humidity of 90% (high temperature and humidity), although content of diffusible hydrogen was as high as 9.5 mL/100 g, cracking rate was 0% and no transverse cracks were generated. Conclusion In the microstructure of weld metal at low temperature and high humidity, proeutectoid ferrite (PF) was more developed and there was side plate ferrite (SPF) growing along the grain boundary, which was more likely to induce the initiation and propagation of transverse cracks. Transverse cracks tended to initiate at the boundary of PF and acicular ferrite (AF), as well as large inclusions. Cracks were prone to propagate in PF, and AF had a certain inhibitory effect on crack propagation. In low temperature and high humidity environment, restraint stress of welded joints was higher, and diffusible hydrogen was more likely to accumulate and cause hydrogen damage, promoting the initiation and propagation of cracks. Conversely, restraint stress of welded joints decreased in high temperature and humidity environment, thus diffusible hydrogen lacked driving force for aggregation, making it less likely to cause transverse cracks.