Against the background of dual-carbon policies and fossil energy shortages, hydrogen energy, as a highly efficient and environmentally friendly clean energy source, has attracted the attention of a wide range of researchers. Hydrogen/air hybrid combustion is essential to promote the large-scale application of hydrogen energy. Hence, the combustion mechanism and measurement technology of key hydrogen/air hybrid combustion parameters have become the current research hotspots. The combustion-air equivalence ratio is a pivotal parameter characterizing the degree of mixing of fuel and oxidant in the combustion process, which directly affects the start of combustion, self-sustainability, and the active degree of combustion chemical reactions. Therefore, real-time online monitoring of the local equivalence ratio in the combustion process is of great significance for improving combustion efficiency and controlling combustion. Currently, relatively few methods can measure the real-time hydrogen/air flame equivalence ratio. As a non-invasive measurement method, Laser spectroscopy can perform real-time online measurement and the characteristics of fast, in-situ, remote analysis, and simultaneous online monitoring of multiple elements. Hence, it has been widely used in the field of combustion measurement. Here, we propose to adopt nanosecond laser-induced breakdown spectroscopy to measure the equivalence ratio of hydrogen/air flames. The experiments were carried out in a premixed hydrogen/air jet flame. The laser was focused into the jet combustion field to generate breakdown and hence plasma, and a spectrometer monitored the plasma emission spectrum. We found that the spectra of H(at 656.3 nm) and O(at 777 nm)are strong, and their intensity shows a regular trend with the change of the equivalence ratio. Therefore, we used the spectra of H(at 656.3 nm) and O(at 777 nm) to label hydrogen and air, respectively, and used their ratios as the measurement coefficients of the fuel-air equivalence ratio. The ratios at different equivalence ratios were measured in a low-velocity flow field with a homogeneous mixture of hydrogen and air, and a calibration curve was established, which we found to be equally applicable to both combustion and non-combustion environments. Based on the calibration curve, we investigated the local combustion equivalence ratios of the jet combustion field in the presence of external doping. In a jet combustion field with an equivalence ratio of 1.0 and a flow velocity of 20 m·s^-1, the variation of the combustion-to-air equivalence ratio at different heights at the jet's center was measured and numerically simulated under the same conditions. The simulations agree with the measurements, and the feasibility of nanosecond laser-induced breakdown spectroscopy for measuring the fuel-air equivalence ratio of hydrogen/air mixtures is verified. This method can provide technical support for the basic research and numerical simulation of hydrogen combustion.