Abstract: The injection of supercritical fluid in the microcellular injection-molding process is a vital procedure, and however the current gas injection system usually generates a gas surge at the beginning of gas injection, which seriously influences the preparation of the single-phase melt and reduces the performance of products. In light of a visual experiment, it is straightforward to prove that the gas surge phenomenon is ubiquitous under different pressure conditions, and therefore the relationship between the gas surge amount and the pressure condition could be obtained.