A lot of stray light spreads in the near field of chemical oxygen-iodine laser, which has serious effects on beam propagation and beam quality control. Measurement methods for different types of stray light are brought out by analyzing and simulating generation mechanisms, types and propagation rules of the stray light. Efficiency for 30 m free propagation is measured by two energy meters. Angular power spectral curve in the channel and scattering energy reflected by the mirror are got by measurement diaphragms. Experimental results show that the energy loss after 30 m free propagation is 5.2%, angular power spectrum increases with propagation distance and deterioration of beam quality increasing. The heat burthens on all diaphragms in the tunnel can be calculated with angular power spectral curve, which lays a good foundation of heat control technology for high energy laser.