Cancer-derived exosomes, as liquid biopsy markers, have been shown to play an important role in the early screening, diagnosis, and prognosis of cancer. However, existing detection methods have shortcomings such as long-time consumption and low sensitivity. Herein, a sandwich-type electrochemical sensing platform based on Prussian blue/graphene oxide (GO/PB) and spiky Au@Fe3O4 nanoparticles was successfully designed and constructed to detect tumor-derived exosomes with high sensitivity and no preprocessing. In this strategy, nanospike structures were introduced on magnetic beads to form spiky Au@Fe3O4, which was used to enrich exosomes from serum, avoiding the extraction and purification processes of previous detections. The enrichment and signal amplification of spiky Au@Fe3O4 could also greatly improve the detection sensitivity of the sensing platform. Consequently, the concentration of exosomes could be directly quantified by monitoring the electroactive molecules of PB. Therefore, the limit of detection (LOD) of the proposed biosensor was 80 particles·μL-1. Furthermore, this proposed biosensor could realize the high sensitivity analysis of exosomes and effectively save detection time, and provide an effective assistant diagnostic tool for the early diagnosis of cancer.