<p>The sand carrying flow in the wellbore is commonly present in reservoirs that are prone to sand production. Even with sand control devices installed, some sand particles produced from the formation will still be carried to the surface by the fluid. The concentration and particle size distribution of sand in the formation are of great significance for the flow law of sand carrying in the wellbore. In this study, computational fluid dynamics and discrete element method coupled simulation method was established to systematically study the relationship between wellbore sand concentration and formation sand production concentration with different well inclination angles, fluid viscosity, particle size distribution of formation sand, and velocity. Firstly, a study was conducted on the influence of different sensitive parameters such as formation sand particle size distribution, fluid velocity, viscosity, wellbore inclination angle, and sand production concentration on wellbore sand carrying capacity. The influencing factors of wellbore cross section sand concentration were obtained. Then, based on the coordination of two subsystems, the formation fluid supply—sand production system and wellbore sand carrying system, and the relationship between the sand concentration in the heterogeneous suspended layer and the formation sand production concentration, a new method for predicting the critical sand production concentration of reservoirs based on the stationary bed theory is proposed from the perspective of the integration of reservoir—wellbore and sand production—sand carrying.</p>