As a liquid biopsy, circulating tumor cells (CTCs) have great significance for the early diagnosis, timely treatment, and practical evaluation of metastasis or recurrence of cancer. However, the enrichment of rare CTCs in complex blood samples is still a significant challenge. Here, unique and highly sensitive folic acid (FA)-functionalized cascade amplification system-modified magnetic nanoparticles (MNPs) were constructed to effectively capture CTCs in whole blood. In this system, as a targeted molecule, numerous FA molecules were conjugated on the surface of PAMAM dendrimers (PAMAM-FA) (first amplification) through a polyethylene glycol (PEG) linker, which could promote the more facile binding of folate receptors (FR) on the surface of ovarian cancer cells (SKOV3 cells). Then, PAMAM-FA was further modified with biotin to fabricate biotin-PAMAM-FA (BPF), which could combine with streptavidin (SA)-modified MNPs (SMs) viathe SA-biotin system to efficiently target and separate CTCs. The capture efficiency of the constructed MNPs-SA ∼ biotin-PAMAM-FA (SM@BPF) nanoprobes was 90.3% with high cell viability (∼93.2%) and minimal non-specific adsorption (∼25%). Moreover, fewer nanoprobes were absorbed on the surface of the SM@BPF-captured SKOV3 cells (one-step method) compared with the SM/BPF-captured SKOV3 cells (two-step method), which was beneficial for further biological analysis. We expect that this recognition molecule-based cascade amplification system will provide an innovative CTCs enrichment platform for the early-stage diagnosis of ovarian cancer.