Out-field laser jamming experiment of varifocal colour CCD imaging system irradiated by semiconductor laser was done. Laser jamming effects of colour CCD imaging system with different focal lengths were measured. Laser jamming model was set-up, and theoretical proving and analysis on experimental results were completed. Theorical and experimental results show that laser jamming effect of colour CCD imaging system irradiated by 750 nm laser is obvious, and CCD surface appears obvious light saturation and crosstalk phenomena. In the same initial laser irradiating conduction, laser power truncated by the aperture gradually decreases with increase of focal length f, and light saturation area on the CCD surface gradually increases. When focal length f of colour CCD imaging system is 17 mm, light saturation area on the CCD surface is 0.33 mm×0.29 mm. While focal length f of colour CCD imaging system increases to 120 mm, light saturation area on the CCD surface is 1.8 mm×1.2 mm. Simulation results are coincident with experimental results, and it proves laser jamming model is correct. The conclusions have a reference value for colour CCD in the practical application.