Striation-free laser cutting of thick section stainless steel is hard to obtain due to several factors, such as nozzle standoff distance, cutting speed, focal plane position, gas pressure, thickness of metal and recast layer. It will be vital to properly combine these factors in striation-free cutting because striation formation is a complicated process. Therefore, many scholars have been studying the mechanisms of striation formation, which will be systematically summarized in this paper. Based on the review, the author holds that supersonic gas nozzle designing plays a key role in creating an ideal cutting condition. Based on the introduction of some structures of supersonic gas nozzle, this paper proposes that two objectives should be fulfilled in order to achieve striation-free cutting: One is to produce a uniform flow of assistant gas and the other is to get a stable laser cutting temperature field.