Several multi-principal element alloy (MPEA) catalysts exhibit the ability to promote the hydrogen evolution reaction (HER) and maintain stability under acidic conditions. Here, we investigated the impact of ordered behavior and surface oxidation of FCC_CoCrFeNi and Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 MPEAs on HER performance through first-principles calculations. The ordering behaviors of MPEAs were described using L12_AuCu3 sublattice model and site occupying fractions (SOFs). And we found that the catalytic activity of single intermediate *H at top or bridge adsorption sites surpassed that at the hollow site. However, the hollow site exhibits strong adsorption towards *H, resulting in the transfer of *H from other sites to hollow site. Meanwhile, compared to those containing only hydrogen, MPEAs with both hydrogen and oxygen exhibit lower overpotentials. Primarily due to oxygen facilitating hydrogen adsorption and subsequent desorption from MPEA surfaces, this fundamental finding highlights the beneficial role of alloy surface oxidation in promoting HER performance. Furthermore, the overpotential values of the three slab models based on SOFs are similar, demonstrating consistent atomic distribution behaviors, thereby better reflecting the overall catalytic performance of ordered MPEAs. These explorations bring new insights into the ordered behavior and surface oxidation of MPEAs in HER catalysis.