In this work, a tetrahedral DNA nanostructure (TDN) designed with multiple biomolecular recognition domains (m-TDN) was assembled to construct an ultrasensitive electrochemical biosensor for the quantitative detection of tumor-associated mucin 1 (MUC-1) protein. This new nanostructure not only effectively increased the capture efficiency of target proteins compared to the traditional TDN with a single recognition domain but also enhanced the sensitivity of the constructed electrochemical biosensors. Once the target MUC-1 was captured by the protein aptamers, the ferrocene-marked DNA strands as electrochemical signal probes at the vertices of m-TDN would be released away from the electrode surface, causing significant reduction of the electrochemical signal, thereby enhancing significantly the detection sensitivity. As a result, this well-designed biosensor achieved ultrasensitive detection of the biomolecule at a linear range from 1 fg mL-1 to 1 ng mL-1, with the limit of detection down to 0.31 fg mL-1. This strategy provides a new approach to enhance the detection sensitivity for the diagnosis of diseases.