The invention provides a flue gas temperature adjusting method, device and system. The method comprises the steps of receiving a boiler load signal to be used as a feedforward signal, receiving a turbidity signal of an outlet of a dust remover to be used as a feedback signal, generating an adjusting signal according to the feedforward signal and the feedback signal, and adjusting the water amount of a heat exchange loop and the operation mode and the parameter of dust remover control equipment through the adjusting signal. The water amount on the heat exchange loop and the temperature of flue gas are adjusted according to the adjusting signal, and meanwhile the operation mode and the parameter of the dust remover control equipment are adjusted according to the adjusting signal. The flue gas temperature of an inlet of the dust remover can directly influence the working efficiency of the dust remover, and thus the flue gas temperature of the inlet of the dust remover can not be too high. In order to achieve environment-friendly emission reduction, the turbidity of the outlet of the dust remover further needs to be limited, and the turbidity of the outlet of the dust remover is used as highest priority feedback information for conducting closed-loop control. The working state of a flue gas waste heat utilization device is considered, and the working state of the dust remover is also considered.