The invention discloses an energy-saving type sewage sludge harmless treatment method. The method includes the following steps of firstly, conducting continuous freezing on sludge through a freeze drying energy circulation system, and unfreezing the sludge after continuous freezing; secondly, conducting dewatering on the sludge, completely processed through freezing and unfreezing, in a filter pressing device, so that sludge with the low moisture content is obtained through filter pressing; thirdly, smashing the sludge in a smashing device; fourthly, conveying smashed sludge particles into a sludge drying device to be dried, dissipating heat through the freeze drying energy circulation system by means of a condenser, and transferring heat to air; fifthly, sending the sludge particles into an incinerator to be incinerated, making generated high-temperature smoke enter a waste heat boiler, making air heated by the condenser enter a second heat exchanger to continue to absorb heat, and unfreezing the sludge and drying the sludge particles through the formed high-temperature air. By means of the method, the sludge processing amount cannot be increased in the treatment process, and due to recycling of working medium energy, the freezing efficiency and the heat utilization rate of the sludge are increased.