The construction of heterojunctions is generally considered as one of the effective strategies to improve gas sensing performance. Herein, the NiO/Al2O3 (NAO) hybrid structure is constructed by calcining Ni–Al layered double hydroxides (NiAl-LDHs). The specific surface area and pore size of NAO are effectively regulated by changing the content of NaOH. The XPS and BET characterization results indicate that NAO-5 exhibits a high oxygen vacancy content, a large specific surface area (468.524 m2 g−1), and abundant pore size. The hydrogen (H2) sensitivity property of NAO was investigated, and NAO-5 exhibited outstanding gas sensing performance to 500 ppm H2 at 370 °C, including high response (10.524), fast response recovery speed (21 and 30 s), and wide detection range (0.1–5000 ppm). The improved gas property is mainly attributed to the increased oxygen vacancies and specific surface area. This study provides a feasible approach for NiAl-LDHs in H2 monitoring and early warning.