With the continuous increase of high power laser，the demand for real-time accurate measurement of laser power in practical applications is becoming more and more significant. The traditional laser power measurement mainly depends on absorption calorimeter. The absorption calorimeter has some common problems，including large volume，slow measurement speed and low measurement accuracy. As a result，it is not suitable for the real-time power measurement of high power laser.The radiation pressure power measurement can effectively solve those problems. Based on the principle of radiation pressure power measurement，this paper designs and develops a rediation pressure power measurement device which can measure laser power up to 6 kW in real time. The device measures the output power of high-power infrared laser at 1 080 nm. The power range reaches 1 kW to 6 kW，the resolution of measurement reaches 50 W，and the measurement stability is better than 1%. The device can meet the real-time and accurate measurement requirements of kilowatt high power laser. The device can monitor the laser power in real-time，and can evaluate the transmission loss. The device will have great research value in the practical applications including high energy laser processing，laser guidance and laser communication.