In space additive manufacturing, the operating environment will experience close to zero gravity. Therefore, it is necessary to understand the gravity effects in laser metal deposition (LMD) for the 3D printing of metal components. In addition, near vacuum condition can be associated with certain space environments. Until now there has been no study reported on the effects of gravity and pressure in LMD for potential space applications. This paper reports an investigation on the development of computational fluid dynamic (CFD) transient models for the understanding of extreme gravity and pressure effects in laser metal deposition process with wire feeding in space. Compound process factors were taken into consideration including material addition, phase change, surface tension, melting and solidification, gravitational force, pressure, temperature dependent material properties and a moving Gaussian heat source. Experimental validation of the model was made by deposition in different orientations on the Earth. The simulation results showed that surface tension would dominate the melt pool dynamics at reduced gravity and thus irregular deposition tracks would appear. Reduction of wire volume deposited per unit length compared with that on the Earth would minimise this effect. As the pressure was reduced, it was found that material vaporization would more likely to occur. It was found that by lowering laser power or increasing scanning speed, material vaporisation could be avoided. (C) 2019 Published by Elsevier Ltd.