Green hydrogen energy developed through electrochemistry is one of the solutions to current energy problems. The less noble metal Ruthenium (Ru) plays an important role in alkaline electrocatalytic hydrogen evolution reaction (HER) as effective electrocatalyst. Nevertheless, the high cost (>110 RMB per gram) hinders the large-scale application of Ru in industrial hydrogen production. Moreover, the strong adsorption of OH* intermediates over Ru limits the electrocatalytic performance in alkaline HER. Here, we report the Mo-doped Ru nanocluster embedded on N-doped carbon framework (RuMo/NC) as alkaline HER catalyst, which shows excellent catalytic performance with an overpotential of 24.2 mV to reach 10 mA cm-2 with only 0.4 wt.% of Ru, much lower than most reported Ru-based catalysts. DFT calculations reveal the introduction of Mo has improved the activity by alleviating the poisoning effect of OH* over Ru in HER. Through fully utilizing Ru in the catalyst, this work marks a step forward in the development of Ru-based catalysts in alkaline HER.