The invention provides a preparation method of an inorganic-organic composite phase-change energy storage material for buildings. The preparation method comprises the purification of diatomite, the preparation of polyacrylic acid-polyacrylamide-sepiolite composite water-absorbing resin and the preparation of a super absorbent resin-inorganic hydrous salt Na2SO4.10H2O composite phase-change energy storage material. The inorganic-organic composite phase-change energy storage material is mixed with building mortar in a certain ratio and then applied to an exterior wall coating, and after solidification, the coating has the function of phase-change energy storage and is also capable of preventing the exterior wall from cracking. Performance tests indicate that the inorganic-organic composite phase-change energy storage material prepared by use of the method has a phase-change temperature at 32.5 DEG C and is still kept stable in a temperature regulating function after heat absorption and heat release for a plurality of times. The phase-change energy storage material prepared by use of the method is mixed with the building mortar to be be widely applied to the exterior wall coatings of the buildings.