Sewage sludge is a semi-solid byproduct of wastewater treatment, with a water content of over 80%. The available methods for disposal and recycling usually require the water content to be within 50%-70%, and sludge dewatering is an important prerequisite for its disposal and resource utilization. In this paper, the structure and composition of water in sludge and the reasons for the difficulty in dewatering residual sludge are analyzed, and the key bottleneck is the effective removal of bound water and intracellular water. The roles and core mechanisms of physical, chemical, and biological pretreatment methods are described; especially, the mechanism, dewatering effects, and combination processes of enhanced residual sludge dewatering by chemical conditioners such as flocculants and filter aids are focused on. The selection principles and application scope of mechanical dewatering equipment for residual sludge are discussed. This paper analyzes the resource utilization approaches of dewatered residual sludge, including the preparation of fertilizer, building materials, biochar, and high-value products. Finally, the key problems that need to be solved in the future are proposed, so as to provide references for the theoretical research and technological application of residual sludge deep dewatering and resource utilization.