The invention relates to a coagulating sedimentation agent for treating low-temperature low-turbidity water and belongs to the field of applied chemistry, in particular to the field of coagulating sedimentation treatment agents of low-temperature low-turbidity water. The coagulating sedimentation agent consists of coaly activated carbon powder and oxidized polysilicate aluminium ferric according to a mass-to-volume ratio (mg/mL) of 1:1 to 10:1. The coagulating sedimentation agent is capable of breaking through the limitation that the sedimentation effects of conventional aluminum and iron salt coagulating agents are greatly influenced by factors such as water inlet temperature, suspended solids and turbidity, is taken as a high-efficiency, economic and environment-friendly coagulating agent for treating low-temperature low-turbidity water generated from power plants and water works and industrial water (living water, wastewater and the like), and has high economic benefits and obvious social benefits.