Entrained gas injection molding, such as structure foam, microcellular foam, gas assistant processing, has some common technical issues and safety concerns which are important to be understood fully for a safe system, and acceptable processing conditions. Several common processing methods available in the market are analyzed for machine and mold design, part design, and processing requirements. Two typical entrained gas processes, gas assistant and foaming, are discussed with both processability and safety. A physical explaining for the safety rules is presented. The single phase solution is the key of all the foaming methods. All necessary modifications are addressed for better gas foaming process.