The results of HONO trace detection using mid-infrared tunable laser absorption spectroscopy technology based on the 8 μm room-temperature continuous wave quantum cascade laser are reported. The characteristics of the device are estimated and described with pure methane gas. Direct absorption spectroscopy is applied to trace gaseous HONO detection via a 125 m long multi-pass cell. The sensitivity of the instrument is evaluated using HONO sample generated by chemical reaction of H2SO4 and NaNO2. The generated HONO concentration is quantified by means of a denuder system associated with a conventional NOx analyzer, and the minimum detectable HONO concentration is found to be about 7.3 μg/m3 in 1 s integrated time. HONO losses resulting from the optical cell wall are experimentally investigated. The rate constant of HONO determined in the present work might be helpful for future field measurements of HONO, especially when an absorption cell is used.