The invention relates to a coal water slurry cyclone entrained flow gasifier and a gasification method thereof, belonging to the technical field of coal gasification equipment. The coal water slurry cyclone entrained flow gasifier comprises a top nozzle, a gasifier roof, a gasification chamber, an exhaust port and a bottom deslagging port, wherein a swirl blade is arranged in the top nozzle; the side wall if the gasification chamber is provided with at least one layer of corner tangential O2 nozzles; coal water slurry is fed through the top nozzle in a swirl manner, and forms a rotary coal water slurry atomized airflow in the gasifier roof region; pure oxygen is introduced through the corner tangential O2 nozzles on the side wall of the gasification chamber, and forms a tangential high-speed rotary airflow in a region close to the gasifier wall; and under the centrifugal action of the high-speed rotary airflow, coal water slurry particles are subjected to film type gasification on a liquid slag film formed on the surface of the gasifier wall. The invention effectively prolongs the service life of the gasifier nozzle, increases the in-gasifier residing time of the coal water slurry and improves the coal gasification carbon conversion rate; the formed liquid slag resides on the wall surface, thereby effectively protecting the gasifier wall from heat damage and chemical corrosion damage; and the corner tangential O2 nozzles are arranged in multiple layers along the height direction of the gasification chamber, thereby ensuring that the temperature field in the gasifier is uniform.