The invention discloses a system for preparing coal water slurry by mixing coke powder with coking wastewater. The system comprises a mixed powder preparing part, a coking wastewater collecting part and a coal water slurry preparing part, wherein the mixed powder preparing part comprises a coal dust preparing unit, a fine coke powder preparing unit and a powder mixing device; the fine coke powder preparing unit comprises a coke powder collecting device, a coke powder transporting device and a coke powder grinding device; the coal dust preparing unit comprises a screening device and a coal dust grinding device; the outlets of the coke powder grinding device and the coal dust grinding device are communicated with the powder mixing device; the coking wastewater collecting part comprises a coking wastewater container and a coking wastewater pipeline; the coal water slurry preparing part comprises a coal slurry tank, a stirring device and an additive adding device; a powder inlet of the coal slurry tank is communicated with the outlet of the powder mixing device; a liquid inlet of the coal slurry tank is communicated with the coking wastewater pipeline; and the outlet of the coal slurry tank is communicated with a gasification furnace. The system disclosed by the invention can comprehensively utilize the coke powder and the coking wastewater.