Objective The number of circulating tumor cells (CTCs) is closely related to the prognosis and survival rate of patients. To study the movement process of CTCs in the blood and the mechanism of CTC capture by CellCollector, and to reveal the relationship between the number of detected CTCs detected and the actual CTC concentration in the body. Methods Based on Fluent and EDEM software, unidirectional fluid-solid interaction method was applied to establish a two-phase flow model, including the hemodynamic model and the CTC transport model, and the capture simulations under several CTC concentration conditions was were carried out. Results The number of CTCs captured by CellCollector is significantly positively correlated with the CTC concentration in the body. When the CTC concentration is low, CTCs can only be captured in a few time intervals, and the capture has a certain contingency; as the concentration increases, the uniformity of CTC captures over time becomes better, and the total number of captures also increases. Conclusion Through the fitting of the simulation results, the analytical quantitative relationship between the number of captured CTCs captured and the CTC concentration in the body is given, which provides a theoretical basis and mechanics explanation for the clinical use of CellCollector.