The invention relates to a construction method of an electrochemical immunosensor with a tri-modified TiO2 nanowire array as a support. The construction method includes the steps that a compact and regular TiO2 nanowire array is synthesized with the hydrothermal method and then modified, a Mo element is successfully doped into the TiO2 nanowire array in the modification process to facilitate the electron transferring capacity, and a MoS2 slice is also successfully deposited on the surface of an electrode; then a chitosan solution is dropwise added to the surface of the electrode of the modified TiO2 nanowire array, and a capturing antibody Ab1 is bound to the surface of the electrode in a covalent mode through a propyl-dimethicone cross-linking agent BS3; meanwhile, a cylindrical TiO2 one-dimensional nanomaterial is prepared with the hydrothermal method and subjected to amination, and then horse radish peroxidase (HRP) and a signal antibody Ab2 are jointly modified on the surface of a TiO2 nanometer column with BS3 as a cross-linking agent to obtain a signal antibody marker. The electrochemical immunosensor prepared with the method can rapidly measure a carcino-embryonic antigen (CEA), sensitivity is high, the linearity range is wide, and the detection limit is low.