2D MXene‐based catalysts, such as Ti3C2Tx have unique, excellent properties and show extraordinary advantages in many catalytic reactions. However, as cocatalysts for photocatalytic hydrogen evolution reaction (HER), MXene has insufficient catalytic activity because the active metal sites of H+ binding are hidden by passivation −F/−O termination, which hinders postreaction desorption of H2. A simple ultrasonic treatment method is used to expose more active sites and adjust the surface work function of Ti3C2Tx, and additionally inactive −F/−O terminal groups are replaced with diaminoethanethiol, denoted as Ti3C2‐Ax, as the surface terminal group through covalent bonds (Ti−S). The optimized photocatalyst (Cd0.4Zn0.6S/Ti3C2‐A40) demonstrates excellent catalytic activity (HER: 13.44 mmol h−1 g−1), which is about 5.8 and 1.9 times higher than that of pristine Cd0.4Zn0.6S and Cd0.4Zn0.6S/Ti3C2 with stability (24 h of cycle experiments), outperforming most of the reported MXene‐based photocatalysts. The results of relevant experiments and density functional theory calculations reveal that the excellent conductivity of Ti3C2‐A40, well‐structured Cd0.4Zn0.6S/Ti3C2‐A40 Schottky junction, and the efficient interfacial charge transfer are major factors that contribute to the improved photocatalytic mechanism. This promotes application of surface‐modified MXene as an efficient cocatalyst and provides a new idea for design and synthesis of heterojunction materials.