The present invention relates to a method for converting and separating vanadium, titanium, and iron from the vanadium-titanium-iron concentrate in one step, which includes the steps as below. (1) The vanadium-titanium-iron concentrate is mixed and roasted together with addition agent and reducing, agent, and thereby vanadium-containing pig iron and vanadium enriched slag are obtained. (2) The vanadium titanium enriched slag is leached in water and filtered, and thereby vanadium-containing solution and titanium slag are obtained. The technical features of the present invention are as below. By the new process of sodium reduction coupling, a new system of low-temperature smelting multiphase reaction separation is constructed. The reduction of iron, sodiumizing of vanadium, and the melting separation process of the vanadium titanium enriched slag and the iron are achieved in one step. Three products, i.e., the vanadium-containing pig iron, the vanadium-containing solution, and the titanium slag are produced.