The invention discloses an electrochemical sensor for detecting lead ions and / or cadmium ions, and a preparation method and an application thereof. The electrochemical sensor includes a glassy carbonelectrode, of which the surface of a reaction terminal is modified by ordered mesoporous carbon supporting hollow spherical bismuth oxide, which is formed with the ordered mesoporous carbon as a carrier, of which the surface supports the hollow spherical bismuth oxide. The preparation method includes a step of modifying the ordered mesoporous carbon supporting hollow spherical bismuth oxide onto the surface of the reaction terminal of the glassy carbon electrode. The electrochemical sensor has advantages of good stability, long service life, wide detection range, low detection limit, good selectivity and strong anti-interference capability. The preparation method has simple processes, low cost and convenient operations, is pollution-free and has extensive application range. The electrochemical sensor is used for detecting lead ions and / or cadmium ions, has simple operation, low cost, short responsive time and high sensitivity, and has great application prospect.