Abstract: In order to analyze the effect of scattering loss on optical transmittance of transparent laser ceramics, the paper uses zeroth-order lognormal distributions(ZOLDs) to describe the scattering loss at different pore sizes and porosities, and introduces the definition of secondary phase volume ratio to calculate the number of scattering particles. The effects of scattering loss due to pores, grain boundary secondary phases and grain boundary surface roughness on optical transmittance of transparent laser ceramics are discussed based on the theories of Mie scattering, Rayleigh scattering and total integrated scatter(TIS). The results show that the transmittance is influenced significantly by porosity, while pore size distributions determine the trend of the envelope of optical transmittance;