The problem of ever‐increasing industrial demand versus the supply shortage of helium (He) is inevitably encountered by scientists worldwide. Membrane‐based separation technology provides an economical method to alleviate the current He scarcity. In this study, using a combination of first‐principles calculations and molecular dynamics simulations, it is theoretically demonstrated that the phosphorus carbide membrane P2C3 possesses high efficiency in He separation from the natural gas (H2, N2, CO, H2O, CO2, and CH4) and other noble gas atoms (Ne and Ar). In addition, the He permeance exceeds 10–4 mol m–2 s–1 Pa–1 over a wide range of temperatures (200–500 K), which is far beyond the industrially acceptable value. Combining the zero‐point‐energy and quantum tunneling effects, the quantum analysis shows that the P2C3 membrane has great potential for 3He/4He isotope separation, thus providing a combined means for both He and 3He isotope separation. The results uncover a new solution of utilizing P2C3 nanomaterial as a novel medium for gas treatment and the findings of this study will promote experimental efforts in the future. [ABSTRACT FROM AUTHOR]