The invention provides a method for directly preparing nano-titania at low temperature by taking industrial titanic liquid as a raw material by diffusion dialysis. The method uses a diffusion dialyzer to recycle the sulfuric acid in the industrial titanic liquid titanium, and the separated industrial titanic liquid with low acidity is prepared into nano-titania powder at low temperature and in liquid phase. The invention has the following reaction conditions: temperature is 40-100 DEG, the reaction time is 0.5-20 hours, and the nano-titania powder can be prepared by the produced mixture through the centrifugal separation, water and alcohol washing several times, and vacuum drying. The invention has the advantages that the preparation cost is low, the sulfuric acid in the raw material can be recycled, the particle diameter distribution of the prepared nano-titania is uniform, and the specific surface area is large. The product can be directly used or can be prepared into the anatase type or rutile type nano-titania powder with higher crystallinity via high temperature calcinations. The technology has low one-time investment, simple preparation operation and low production cost. The method belongs to the production technology with environment protection characteristic and sustainable development characteristic.