Steam generator passive heat removal system(SG-PHRS) is used as a passively safe mode to provide decay heat removal in some advanced pressurized water reactors. Due to the structure characteristics of steam generator(SG), there are two natural circulation loops coupling in SG-PHRS in case of a safety-related event. The existing natural circulation scaling criteria could be used to simulate the natural circulation inside SG. Two-phase natural circulation loop is studied carefully, and the dominant effects of SG on behaviors of natural circulation in passive heat removal system are presented. Based on the understanding of SG-PHRS operation, system pressure transient scaling and two-phase natural circulation scaling are analyzed by establishing the relevant continuity,integral momentum and energy equations in one-dimensional area-averaged forms. With modified equations,similarity criteria for SG-PHRS are obtained for engineering application. In addition, equal height simulation and reduced height simulation are studied. Steam generator passive heat removal system (SG-PHRS) is used as a passively safe mode to provide decay heat removal in some advanced pressurized water reactors. Due to the structure characteristics of steam generator (SG), there are two natural circulation loops in SG-PHRS in case of a safety-related event. The existing natural contingency criteria could be used to simulate the natural circulation inside SG. Two-phase natural circulation loop is is viewed carefully, and the dominant effects of SG on behaviors of natural circulation based on the understanding of SG-PHRS operation, system pressure transient scaling and two-phase natural scaling is established by the relevant continuity, integral momentum and energy equations in one-dimensional area-averaged forms With modified equations, similarity criteria for SG-PHRS are obtained for engineering application d height simulation are studied.