Abstract: Nuclear fuel cladding constitutes the primary safety barrier in pressurized water reactors (PWRs). The performance of the fuel cladding critically governs reactor safety and economic viability. Zirconium alloys, which are the only commercially deployed fuel cladding material in PWRs, exhibit corrosion behavior in high-temperature aqueous environments, which is the main factor that limits fuel assembly service life. Variations in primary coolant chemistry significantly modulate zirconium alloy corrosion and the dissolved hydrogen are considered as a key water chemistry parameter. Although hydrogen is routinely added to suppress water radiolysis and mitigate structural material corrosion, the specific effects of dissolved hydrogen on zirconium alloy corrosion under high-temperature, high-pressure water conditions remain insufficiently studied, and consensus on hydrogen’s mechanistic role is lacking. This study investigated the in-situ corrosion behavior of the domestic N36 zirconium alloy under four dissolved hydrogen concentrations (0, 2, 20, and 40 cm³/kg) in simulated PWR water conditions. Through high-temperature in-situ electrochemical measurements, including polarization curves and electrochemical impedance spectroscopy (EIS), combined with advanced characterization techniques, including scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the corrosion behavior of N36 zirconium alloy and the microstructure of the corroded oxide film were analyzed. This research obtains in-situ information on the oxide film growth and electrochemical corrosion dynamics and impedance characteristics during the initial corrosion stage of N36 zirconium alloy under varying water chemistry conditions. This study analyzed and discussed the impact mechanisms of dissolved hydrogen on the corrosion behavior of N36 zirconium alloys. Similar to the results of other zirconium alloy corrosion studies, N36 zirconium alloy exhibits an initially elevated corrosion rate that gradually decreases and stabilizes. The mechanism of the hydrogen evolution reaction in the initial stage of corrosion is the Tafel-Volmer mechanism. Notably, the results show that an increase in dissolved hydrogen concentration leads to a positive shift in corrosion potential, and this positive shift becomes more pronounced with increasing dissolved hydrogen concentration. And the dissolved hydrogen increases the corrosion rate of N36 zirconium alloy. The impedance spectrum shows double capacitive reactance, and the capacitive arc increases significantly with the increase of corrosion time. After 14 days of corrosion, oxide films formed at 0 and 2 cm³/kg dissolved hydrogen exhibit semi-infinite diffusion behavior, indicative of protective layer formation. Conversely, at 20 and 40 cm³/kg dissolved hydrogen, oxide films primarily displayed finite-layer diffusion characteristics, dissolved hydrogen significantly reduced both charge transfer resistance and oxide film diffusion impedance, reflecting diminished ionic diffusion resistance and persistently active corrosion. Reduced diffusion constants under high dissolved hydrogen conditions are attributed to hydrogen accumulation at the oxide/metal (O/M) interface, accelerating oxygen diffusion. In addition, the elevated dissolved hydrogen hinders the formation of the corrosion-resistant t-ZrO₂ phase is also responsible for the acceleration of corrosion.