The invention relates to a mechanical-adjustment intake/exhaust guide system of a ventilation air methane (VAM) heat countercurrent oxidation device. The system comprises two intake/exhaust port expansion sections, two intake/exhaust cavities with openings in one ends and a reaction chamber, wherein a first guide plate is arranged in each intake/exhaust cavity; a second guide plate is additionally arranged in each intake/exhaust port expansion section; a set of first mechanical adjustment mechanism is additionally arranged on the outer upper wall of each intake/exhaust port expansion section; a set of second mechanical adjustment mechanism is additionally arranged on the outer side wall of each intake/exhaust cavity; and the rotation of the first guide plates and the second guide plates is adjusted and controlled by the second mechanical adjustment mechanism and the first mechanical adjustment mechanism, respectively. In the invention, the inclination angles of the guide plates can be flexibly adjusted through the mechanical adjustment mechanisms in an actual working condition of relatively great fluctuation of air inflow, and the system has relatively good adaptability to different intake working conditions so as to guarantee uniform distribution of air inflow and temperature of the reaction chamber and improve the operation reliability of the device and the VAM oxidation rate.