The invention discloses a variable-track-gauge wheel set and a locking mechanism thereof. The locking mechanism of the variable-track-gauge wheel set is arranged between a wheel hub and a wheel axle and used for locking wheels at different positions of the wheel axle to adjust the distance between the two wheels. A guiding structure for guiding the wheels to move axially is arranged on the wheel axle, and the locking mechanism adjusts the wheels to designated positions and then locks the wheels at the designated positions. On the premise that a variable track gauge is achieved, it is ensured that the wheel set has enough flexibility, reliability and accuracy.