The invention discloses a preparation process for a composite fertilizer and relates to the technical field of fertilizers. The preparation process comprises four processing steps: preparation of a crosslinked potassium acrylate polymeric original liquid, preparation of a product A, preparation of a product B and acquisition of a finished product. Raw materials of the composite fertilizer are low in cost and long in storage time, a mutual promotion effect of water and the fertilizer is facilitated, the utilization efficiency of water and the fertilizer is improved, and the composite fertilizer has a certain effect on rot and moth of fruit trees. The composite fertilizer is simple in production process and convenient to operate, is a pure natural green fertilizer which is high in quality, high in content and high in utilization ratio, and has a relatively good economical benefit. The output of crops can be greatly improved, and the fertilizer is suitable for the demand of wide farmers and has a huge development prospect.