To investigate the influence of the front and rear blade tip clearances on the performance of a transonic tandem rotor, numerical simulations were employed to analyze the performance parameters and flow field structures of an outlet-stage tandem rotor under various clearance combinations. The study revealed that as the blade tip clearance increases, the margin of the tandem rotor decreases to varying degrees. The changes in both the front and rear blade tip clearances have a basically linear additive effect on the margin, with the margin being more sensitive to the front blade clearance. The leakage flow rate of the front blade is influenced by factors such as the front blade clearance, operating conditions, and rear blade clearance, whereas the leakage flow rate of the rear blade only varies with its own blade tip clearance. At the design point, the values of both the front and rear blade tip clearances impact the rotor tip vortex structure. With a smaller front blade tip clearance, rotor stall is caused by the rear blade blockage resulting from the combination of the leakage flow after the front blade shock and the rear blade leakage flow. With a larger front blade tip clearance, rotor stall occurs due to partial blockage of the front blade passage by the front blade leakage flow and a larger volume of front blade leakage flow leading to a large downstream low-speed region. An increase in the rear blade tip clearance does not change the cause of rotor stall but exacerbates downstream blockage, leading to earlier stall occurrence.