The invention discloses a method for preparing a metallic nickel-loaded catalyst by using an ion exchange process. The method comprises the following three steps: preparation of a nickel sulfate solution; adjustment of the pH value of a nickel-containing solution; and preparation of the nickel-loaded catalyst. Compared with the prior art, the method provided by the invention has the advantages of usage of more widely available raw material and mild reaction conditions. The invention also discloses a method for catalyzing gasification of biomass by using the metallic nickel-loaded catalyst prepared in the invention. Compared with conventional synthetic methods and products, the catalyst prepared by using the method provided by the invention has the advantages of high conversion rate, substantially reduced carbon deposition, long service life, high selectivity and stable activity in a long period of time.