Radiative sky cooling (RC), a passive cooling strategy, can emit the waste heat from the earth into outer space to cool itself or practical objects. Despite it has great potential for energy saving and environmental protection, the low energy density of RC technology and its dependence on atmospheric conditions have limited its practical application. To enhance the cooling capacity of the RC system, concentrated RC systems have been developed. In this study, a compound parabolic concentrator (CPC) is put forward as the concentrator for the concentrated RC system, and a modelling approach to investigate its cooling performance is developed. Previous outdoor experiments have demonstrated the CPC can block a portion of daylight and undesirable external radiation, while effectively concentrating the thermal radiation emitted by the emitter, thereby enhancing the RC performance. Building upon these findings, the amount of light emitted from the RC emitter reaching different annular intervals is simulated using the optical software Photopia. The equivalent sky emissivity can be calculated by the simulated light ratio, and the net cooling power of various models is further deduced. Through the investigation of relevant parameters in the mathematical model, the key factors influencing the cooling power of the RC systems are analysed and determined, providing further evidence of the cooling advantages offered by the CPC-RC system.