The flow field and infrared radiation characteristics of three nozzle for the rocket motor are numerically investigated. The interaction of three jets ejected from three nozzle is analyzed and the flow field is obtained. When the jets are ejected from nozzle exits under the condition that the jet pressure is higher than the back pressure, the inflation of jets happens and the jet boundary contracts inward, thus producing the compression wave to suppress the over-expansion due to the reduction of pressure. Then compression wave expands and enhances for shock. And the expansion and compression wave zone size decreases, as well as intensity weakens along streamwise direction. Once the distance from the nozzle exit reaches 26 times of nozzle diameter, the three jets are merged together to form a jet. The plume infrared radiation distribution of the three-nozzle is similar to that of the single nozzle. It is evident that the total infrared radiation distribution in horizontal plane is different significantly from that in the vertical plane for the three-nozzle.