Atmospheric plasma can induce chemical reactions, and nitric oxide (NO) is one of the main products of atmospheric chemical reactions. Accurate measurement of atmospheric concentration of NO is helpful for revealing the mechanism of atmospheric chemical reactions and optimizing the application of plasma in the atmospheric environment. In this work, NO is generated through atmospheric chemical reactions induced by filament plasma produced by ultrashort laser pulses with a pulse width of 35 femtoseconds and a working wavelength of 800 nm in a sealed absorption cell under variable air pressure. Then, mid-infrared laser absorption spectroscopy is used to measure NO in real time and in situ at variable pressure. It is found that under different air pressures, the concentration of NO produced increases with the reaction time until it remains stable. However, it requires more time for NO to reach a steady concentration with the increase of air pressure. Due to the influence of three-body recombination, the accumulated volume ratio concentration of NO decreases from more than 400 × 10^-6 at low pressure to about 120 × 10^-6 at atmospheric pressure.