Abstract: High power laser system need to be run in a clean environment. If the surface of the optical element attached pollutants in the work process,it will do a damage to the optical components and lead to decline in the load capacity of the entire system. The mechanism of laser affecting to materials which produced particles was analysed. The theoretical basis for the assessment was probed. The requirement and method of measurement was discussed. The contaminant particles which exist in the system surface were measured and analysed. At last,we proposed the technical approachto carry out measurement and assessment of contaminant particles in the high power laser systementirely and deeply.