PURPOSE: To provide a sludge removing method by pressure pulse more effective than conventional ones for removing sludge and deposits from the interior of a heat exchanger.

CONSTITUTION: This method comprises steps of introducing a liquid into a container 5 such as a steam generator, and generating a succession of pressurized pulses of gas in the liquid in order to create shock waves for liberating and removing sludge and deposits 32 from the interior of the container, and the liquid includes a cleaning agent formed from at least one of surfactants, dispersants, thixotropes and separating agents such as flotation agents to accelerate fluidization of the sludge and deposits and prevent these substances from recoagulating.