A set of Mid-IR laser far-field power measurement system based on imaging method is designed and developed. The basic principle of imaging method for measuring far-field laser power density distribution is introduced. The diffuse-reflective board is used to collect laser power distribution information to a Mid-IR thermal imager. And a power detector is installed on the feature position of the board to fuse spot image grey information and actual power value measured by a laser power probe. And the mapping relationship between grey value and power density is obtained to estimate laser far-filed power density distribution. The system has low measurement error and it is simple, reliable and suitable for Mid-IR laser far field power density distribution measurement under different conditions, which can meet the present measurement requirements of high-power IR laser jamming equipments.