The formation of a flammable vapor cloud following a spill of cryogenic liquids, e.g., ammonia and LNG, on a ground or water includes significant toxic, fire, or explosion hazards. The ability to predict the consequences of such an event is crucial to perform proper risk assessment. A boiling model, as one part of the source term modeling of cryogens, was developed using computational fluid dynamics (CFD) codes. Using the model, different boiling phenomena, including film boiling, transition boiling, and nucleate boiling were identified. The vaporization rate can be calculated depending on the ground temperature. The boiling model by CFD method can give a more accurate result than integral models or empirical correlations, especially when a complex geometry of the spill and surrounding was considered. Based on the boiling model, the pool formation and vaporization during cryogenic liquid spill on ground and/or water were studied. Liquid nitrogen was chosen as a safe analogue. The effects of the surface type (ground or water), hot surface conditions (temperature, slope, etc), weather conditions, and two-phase boiling flow rate were discussed and compared with experiments or/and literature data. This is an abstract of a paper presented at the 2012 AIChE Spring Meeting and 8th Global Congress on Process Safety (Houston, TX 4/1-5/2012).