The invention relates to a method for decolorization of sugar juice with water-soluble magnesium salt-lime. The specific steps include: adding a water-soluble magnesium salt into sugar juice, then regulating the pH value with lime milk, performing stirring continuously at certain temperature, then adding zinc polysilicate, conducting stirring at different speeds for certain period of time respectively, and performing flocculation sedimentation to a stable state, thus obtaining clear juice. The invention provides the water-soluble magnesium salt-lime method for clarification and decolorizationof sugar juice, zinc polysilicate is adopted as a flocculant, the decolorization rate is up to 92.21%, also the process is simple and low in cost, does not adopt toxic or harmful substances, belongs to a green clarification and decolorization process, and has important application prospect in the sugar industry. The principle of the method provided by the invention lies in that: a magnesium salt serves as an inorganic decolorizing agent for coagulation reaction under an alkaline condition to generate magnesium hydroxide, non-sugar substances in sugar juice are adsorbed or embedded, then zinc polysilicate is employed as the flocculant for flocculation and clarification, so that a satisfactory result can be achieved.