The visibility errors induced by the multiple-scattering effects are further discussed considering the system parameters of the laser transmissometers, which have been regarded as promising visibility meters used in airports around the world. Based on the size distributions of the advection fog and radiation fog, the transmission of photons is simulated numerically using the Monte-Carlo method. It is noted that the multiple-scattering effects would become more serious for larger water content of the fog, which may cause significant visibility errors as the outputs of the transmissometers. The relative error of transmittance of radiation fog is even possible to achieve 116.76%, and the error of visibility caused by multiple scattering of radiation fog is 19.30% when the diameter of receiver is 100cm. The simulation results further reveal that reducing the receiver aperture may sufficiently suppress the multiple-scattering effects. It is necessary to consider the multiple-scattering effects on the visibility measurement especially for the low-visibility atmosphere, e.g., in dense fog and haze, which gives us important hints on the visibility measurement of laser transmissometers in dense fog and haze.