The invention provides a waterproof sealing prefabricated directly-buried compensator heat insulation product and a prefabricating method thereof. The waterproof sealing prefabricated directly-buried compensator heat insulation product comprises a compensator and an external heat insulation sealing structure of the compensator; the external heat insulation sealing structure of the compensator comprises polyurethane heat insulation layers, soft and flexible heat insulation layers, alarming lines, pressing covers, sealing filler and external protective sleeve pipes; the corresponding polyurethane heat insulation layers are fixed to the fixing end of the compensator; the compensation segment of the movable end of the compensator is wrapped by the soft and flexible heat insulation layers; the corresponding polyurethane heat insulation layers are sequentially fixed to the movable end of the compensator; the compensator, the soft and flexible heat insulation layers and the polyurethane heat insulation layers are sleeved with the external protective sleeve pipes; the two ends of each external protective sleeve pipe are connected with the corresponding pressing cover through bolts; sealing cavities among the external protective sleeve pipes, the pressing covers and the polyurethane heat insulation layers are filled with the sealing filler; and the alarming lines are laid along the compensator and embedded in the polyurethane heat insulation layers and the soft and flexible heat insulation layers. The waterproof sealing prefabricated directly-buried compensator heat insulation product is free of leakage and safe and reliable in running. By means of installing and running of a pipeline leaking monitoring system, the compensator is effectively brought into a monitoring range.