The work aims to explore effects of citric acid concentration, sodium tungstate concentration in sulphate bath as well as plating heat treatment process on tungsten content in nickel tungsten alloy plating, plating hardness, plating microstructure and phase composition. Ni-W alloy platings of certain thickness were prepared different bath composition on low carbon steel in alloy electrodeposition method. Later the platings were treated in different heat treatment processes. Microstructure of the platings was observed with scanning electron microscopy (SEM) , and tungsten content of the plating was detected by its built-in EDS energy spectrum. Phase composition, grain size and lattice distortion of the platings were analyzed by X-ray diffractometer (XRD). Hardness of the alloy platings was tested with micro hardness tester. With the increase of sodium tungstate concentration or decrease of citric acid concentration in the bath, tungsten content in the plating increased, grain size decreased and Vickers hardness increased. Heat treatment atmosphere had little effect on hardness of the platings, but it could change microstructure of the platings, hardness of the platings first increased and then decreased with the increase of heat treatment temperature and holding time. When the bath contains 45 g/L sodium tungstate and 45 g/L citric acid, the obtained plating is substitutional sosoloid Ni17W3 with Ni as solvent and W as solute. In this process, the plating is smooth and crack-free, and hardness of the plating is 894 HV0.1 after later heat treatment for 1.5 h under the protection of argon at 400 ℃.