The invention discloses a scale inhibition device of a water heater and the water heater. The scale inhibition device of the water heater comprises a tank body, a scale inhibitor release part and a connecting base body; an accommodating cavity is formed in the tank body; the lower end of the tank body is provided with an opening; the scale inhibitor release part is arranged on the top of the accommodating cavity; the connecting base body is in butt joint to the lower end of the tank body; a main channel, a water compensating channel and a water draining channel are arranged on the connecting base body; in a water flow direction, the main channel sequentially comprises an inlet section, a throat and a diffusion section; the water compensating channel communicates with the inlet section and the accommodating cavity; and the water draining channel communicates with the diffusion section and the accommodating cavity. The scale inhibition device of the water heater can achieve good scale inhibition effect and good descaling effect on the water heater.