The invention relates to a runway substrate of a treadmill, which is mainly characterized in that: side frames are fixedly arranged on both sides of a bottom board respectively; a pedal frame is arranged on each side frame; each pedal frame consists of an anti-slip frame and a rib; the anti-slip frames are fixedly arranged on the tops of the opposite side frames; an anti-slip element can be arranged on each anti-slip frame; and the ribs are connected with and arranged on the side not opposite to the bottom boards of the anti-slip frames. Therefore, the constructed runway substrate can increase the width of a runway to the maximum and improve the whole practicability.