The invention discloses preparation and application of an alpha-fetoprotein photoelectrochemical competitive immunosensor based on a double-sensitized structure. A sensing interface is constructed byusing titanium dioxide mesocrystals as a probe substrate and immobilizing an alpha-fetoprotein antibody (Ab), and using bismuth sulfide as an electrode substrate and immobilizing an alpha-fetoproteinantigen; the sensor with the double-sensitized structure is constructed by means of specific binding between an antigen and the antibody. An electrode modified with the alpha-fetoprotein antigen is placed in a mixed solution containing different concentrations of free antigen and a certain amount of labeled probes, and the free target antigen competes with the immobilized antigen for bonding to the labeled probes. Under the illumination condition, the electrode bonded with the probes can generate photocurrent with certain intensity, and the amplification of a current signal is realized by means of the double-sensitized structure. Furthermore, as the concentration of the free target material increases, the number of the probes bonded to the immobilized antigen decreases, and the photocurrent intensity is also reduced. Based on the phenomenon, a photoelectric analysis method for alpha-fetoprotein can be established.