The invention discloses a crude-liquid filtering and refining method by a Bayer process and relates to an improvement on the crude-liquid filtering and refining method in the oxidation and production process. The crude-liquid filtering and refining method comprises the following steps of: adding a filter aid being lime milk into the crude liquid in the Bayer process and adopting a leaf filter to carry out filtering and refining on the crude liquid. The crude-liquid filtering and refining method is characterized in that coal ash as the filter aid is also added in the filtering and refining process of the crude liquid. The crude-liquid filtering and refining method disclosed by the invention has the advantages that sodium aluminate refined liquid seston is controlled to be below 0.012g/l, the consumption of lime and the loss of alumina in the refining process of sodium-aluminate crude liquid are reduced, and the deliquation of the system concentration caused by carried water in ashing is reduced; and simultaneously, waste in a boiler of a thermal power plant is applied in the filter aiding of the sodium-aluminate crude liquid, so that the production cost and the waste discharging amount are reduced.