Molybdenum disulfide (MoS2) has attracted considerable attention in electrocatalysis for hydrogen evolution reaction (HER). Nevertheless, its HER activity is far from that of platinum-containing electrocatalysts. Therefore, it is urgent to develop a novel strategy to simultaneously increase the number of active sites (N-AC) and decrease charge-transfer resistance (RCT) to favor HER. Herein, we have demonstrated an efficient approach to etching oxygen-incorporated MoS2 (O-MoS2) nanosheet arrays on carbon cloth for excellent electrocatalytic hydrogen evolution. The influence of temperature (T) at the etching stage and the concentration of ammonium fluoride ([NH4F]) on the micro-structure and HER activity of the as-obtained catalysts have been systematically investigated. The higher etching temperature or [NH4F] is achieved; the faster etching kinetics is obtained. At slow etching kinetics, the etching degree of O-MoS2 nanosheets is relatively low, which cannot supply sufficient unsaturated sulfur atoms for HER. At fast etching, the balance between active site and electron transfer for these etched nanosheets is achieved, which is available to efficient HER. However, excessive etching leads to inefficient HER because of the unsatisfactory RCT. The optimized elctrocatalysts exhibit the superior HER activity among all samples, accompanied by excellent catalytic stability. Therefore, this work promises important application in production of hydrogen.