The invention discloses a preparation method for alendronate sodium, and belongs to the technical field of medicine synthesis. The key points of the technical scheme provided by the invention are as follows: the preparation method for the alendronate sodium comprises the following steps: sequentially adding 4-aminobutyric acid, phosphorous acid and ionic liquid in a reaction kettle, adding phosphorus trichloride when heating to 60-65 DEG C, controlling the temperature to be 55-65 DEG C for reacting, and refining to obtain white crystalline powder alendronate sodium trihydrates. According to the preparation for the alendronate sodium, a new medicine alendronate sodium is synthesized by taking the ionic liquid as a reaction medium; compared with the prior art, the preparation method for the alendronate sodium has the advantages that the reaction conditions are mild, operations are simple, products are easy to separate and purify, the yield and the purity are high, the residual quantity of related substances and organic solvents is small and the medical standards are met, the environment friendliness is achieved, and the ionic liquid can be utilized as the reaction medium and also has a catalytic effect.