In order to ensure the sub-molten salt project to achieve production and efficiency, the processes of liquid phase oxidation of vanadium slag, liquid?solid separation, crystallization of sodium vanadate and three-effect evaporation were systematically studied. The experimental results showed that under the combined action of nano-micro aeration oxidation and scale-up effect, the sub-molten salt demonstration project can achieve the simultaneous extraction of vanadium and chromium at low temperature (140~180℃) and low pressure (0.6~1.0 MPa), the leaching rates of vanadium and chromium were 93% and 85% respectively. Nano-micro-aerated sub-molten salt technology showed excellent leaching performance for vanadium slag from different raw materials. The automatic vertical filter press adopted three-stage counter-current washing mode, which ensured that the water content of tailings was less than 30wt%, the vanadium content was less than 0.15wt%, and the chromium content was less than 0.05wt%. The crystallization rate of sodium vanadate reached 61.5% by using OSLO cooling crystallizer, and the concentration of circulating alkali solution was increased from 45wt% to 50wt% by adding a temperature and pressure reducer at the steam interface of the three-effect evaporation system. In addition, the leaching of vanadium and chromium from vanadium?chromium mud produced during the treatment of wastewater from traditional sodium roasting process was studied by using submerged salt production line. The efficient leaching of vanadium and chromium from vanadium?chromium mud was achieved under the conditions of reaction temperature of 175℃, reaction pressure of 0.65 MPa and feed-in and feed-out speed of 0.25 t/h. The leaching rates of vanadium and chromium were 93.68% and 96.76%. When the concentration of chromium in solution reaches 25~30 g/L, the crystallization process of sodium chromate can ensure that all the chromium dissolved in each liquid phase oxidation reaction was precipitated, and the crystallization rate of sodium chromate was 17.65%.