Objective To study movement process of circulating tumor cells (CTCs) in the blood and mechanism of CTC capture by CellCollector, and reveal relationship between the detected CTC numbers and the actual CTC concentration in the body. Methods Based on Fluent and EDEM software, the unidirectional fluid-solid interaction method was applied to establish a two-phase flow model, including the hemodynamic model and the CTC transport model, and capture simulations under different CTC concentration conditions were conducted. Results The number of CTCs captured by CellCollector was significantly positively correlated with the CTC concentration in the body. When the CTC concentration was low, CTCs could only be captured in several time intervals, and the capture had a certain contingency; as the concentration increased, the uniformity of CTC capture over time became better, and the total number of captures also increased. Conclusions Through the fitting of simulation results, analytical quantitative relationship between the captured CTC number and the CTC concentration in the body is preliminarily given, which provides theoretical basis and mechanical explanation for the clinical use of CellCollector.