A water tank assembly for a robot vacuum cleaner and a robot vacuum cleaner are provided. The robot vacuum cleaner includes a main unit, two drive wheels and a universal wheel. The water tank assembly includes a water tank and a support part, and the universal wheel and the water tank assembly are disposed to the main unit. When the robot vacuum cleaner is located on a horizontal ground, the universal wheel and the two drive wheels contact the ground, and the support part is spaced from the ground by a preset value. When the robot vacuum cleaner is inclined towards a side where the water tank assembly is, the support part contacts the ground.