The presence of sea fog greatly affects both the reflected and transmitted detections when radiation propagates through targets and maritime backgrounds. Thus, the maritime target detections and the remote sensing in oceanic environments would be disturbed by the sea fog. In our work, a poly-disperse sea fog system is introduced. Such a sea fog layer comprises spherical water particles of different radii, where the radii are divided into eight radius regions. The attenuation, asymmetry factors, and absorption probabilities of the radiation interacting with sea fog particles in each radius region are computed using Mie theory. The scattering processes of the radiation in the poly-disperse sea fog layer are traced in our improved Monte Carlo (MC) simulation. This paper presents a new method (named "our method" hereafter) with the intention to provide more accurate calculations on the reflection and transmission when radiation propagates through poly-disperse sea fog media of two different refractive indices. Therein, we investigated the influence of liquid water contents and thicknesses of the poly-disperse sea fog layer on the reflectance and transmittance of the radiation. The results using our MC method compared with those using the previous MC method are also presented. Besides, with three different MC methods along with our method and the previous method, we also inspected how different MC methods affect the calculations of reflectance and transmittance, and it shows manifestation that our method has an advantage over the previous method. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement