Though much work has been done concerning quantum radar cross section (QRCS), the related question about quantum radar scattering characteristics of targets in the atmospheric medium has not been considered. Understanding this question is of primary significance in the military and civil fields of quantum radar. The main objective of the paper is to propose a new algorithm for the calculation of QRCS in homogeneous atmospheric medium (M-QRCS). Therefore, based on the chain of beam splitters proposed by M. Lanzagorta to describe homogeneous atmospheric medium, the photon attenuation model is established, the photon wave function is modified, and the M-QRCS equation is proposed. Furthermore, in order to obtain an accurate M-QRCS response, we carry out simulation experiments on a flat rectangular plate in the atmospheric medium composed of different atomic arrays. Based on this, we study the influence of the attenuation coefficient, temperature, and visibility on the intensity of the peak value of main lobe and side lobes of M-QRCS. In addition, it is worth noting that the numerical calculation method proposed in this paper is based on the interaction between photons and atoms on the target surface, so it is suitable for the calculation and simulation of M-QRCS for targets of any shape.