Molecular-imprinted polymers (MIPs) are generally considered as substituents for natural antibodies. MIPs synthesis needs to select appropriate functional monomers. Because of its strong interaction with the template, antibody–antigen complexes can be formed before polymerization. In this paper, myoglobin (Mb)-imprinted polymers with a new sulphoxide monomer (2-(methylsulphonyl) ethyl acrylate, MSEA) as functional monomers were successfully prepared via electrochemically mediated atom transfer radical polymerization (eATRP). At the same time, to solve the problems of low selectivity and large template size limitations, the Mb-imprinted polymers were prepared on the surface of Au electrode decorated with three-dimensional foam graphene (FG) and nano Au (nAu). Cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscope and X-ray photoelectron spectroscopy were used to characterize the Au electrode modified with Mb-imprinted polymer (Au/FG/nAu/MIP$_{MSEA}$). The prepared Au/FG/nAu/MIP$_{MSEA}$ electrode was used as an electrochemical sensor to detect Mb. The results of experiments showed that the proposed biosensor had good selectivity, reproducibility, repeatability and stability. The linear response range was from 1.0 ${\times}$ 10$^{-12}$ to 1.0 ${\times}$ 10$^{-1}$ mg.l$^{-1}$, and the detection limit was 1.21 ${\times}$ 10$^{-13}$ mg.l$^{-1}$ (S/N = 3). Compared with other methods for detecting Mb, the sensor had a wider detection range and lower detection limit.