The present invention discloses a transition metal nano-catalyst, a method for preparing the same, and a process for Fischer-Tropsch synthesis using the catalyst. The transition metal nano-catalyst comprises transition metal nanoparticles and polymer stabilizers, and the transition metal nanoparticles are dispersed in liquid media to form stable colloids. The transition metal nano-catalyst can be prepared by mixing and dispersing transition metal salts and polymer stabilizers in liquid media, and then reducing the transition metal salts with hydrogen at 100-200° C. The nano-catalyst can be used for F-T synthesis reaction. The process for F-T synthesis using the nano-catalyst comprises contacting a reactant gas mixture comprising carbon monoxide and hydrogen with the catalyst and reacting. The catalyst can rotate freely in three-dimensional space under reaction conditions, and have excellent catalystic activity at a low temperature of 100-200° C. Those reaction conditions are much milder than those for current industrial catalysts for F-T synthesis (200-350° C.). In addition, the transition metal nanoparticles have smaller diameter and narrower diameter distribution, which is beneficial to control product distribution. Meanwhile, the catalyst can be easily separated from hydrocarbon products and reused. All of the above merits imply the broad application prospects of the transition metal nano-catalyst.