The invention provides a washing machine as well as a control method and a control device of the washing machine, and aims to solve the problem that too much or too little washing agent is added into the washing machine in the prior art. The control method of the washing machine provided by the invention comprises the following steps of: detecting a conductivity parameter Vt and a temperature value T of water for washing; utilizing the temperature value T to carry out compensation calculation on the temperature value T to obtain a conductivity compensation value V0; judging a water hardness according to the conductivity compensation value V0 and revising an adding parameter of the washing agent according to the water hardness; and adding the washing agent according to the adding parameter of the washing agent. According to the technical scheme disclosed by the invention, the conductivity and the temperature value of the water for washing are detected to carry out the compensation calculation on the conductivity, so as to judge the water hardness of the water for washing; the corresponding washing agent can be added according to the hardness and the corresponding washing agent is added according to the water condition of the water for washing; and under the condition of guaranteeing the washing quality, the use amounts of the washing agent and the water for washing are saved.