The invention relates to the technical field of heating equipment, and particularly relates to a horizontal electric water heating device. The horizontal electric water heating device comprises a shell, a liner and an insulation layer. A magnesium rod, a water outlet pipe, a water inlet pipe, a water distributor, a heating pipe, a temperature controller and a fireproofing controller are arranged at the bottom of the shell. The insulation layer is composed of a leveling layer, a rigid foam polyurethane layer, a waterproof slurry layer, a fiberglass mesh, a putty layer and a paint decoration layer which are arranged in sequence. An outer coating comprises a first water-soluble organic composite coating agent and an epoxy back paint layer. An inner coating comprises a second water-soluble organic composite coating agent, a polyester top coat layer and a protection film layer. The horizontal electric water heating device has the characteristics of being simple in structure and good in insulation effect and corrosion-resistant effect.