The 1064 nm laser backward scattering theoretical models of single particle and water fog particles with size distribution are studied. According to scattering parameters and scattering phase function related to scattering cross section and Stocks vectors,total scattering phase function of water fog particles with size distribution are calculated and obtained through the weighted function of particles size distribution. For laser backward scattering angle between 150°~180°,the sparse large water fog particles have single scattering feature,while water fog particles with the mixed size distribution have large backward scattering effect. The water fog generating equipment and laser backward scattering testing system are designed,including electro-optical detector,attenuator sets,mirrors,polarizing films,etc. The special designs are used to reduce environment’s effects,such as independent incident and outgoing window,rear reflector and the inner wall extinction. The laser backward scattering effect of water fog particles is measured by using this device,and the gotten results are consistent with theoretical value. The results show that the laser backward scattering of water particles is a complicated dynamic process,and it is related to the absorption and scattering of water fog particles with different size distributions in propagation path.