The invention discloses a detection device for the nitrogen oxide content of a gas, which is used for detecting the concentration of nitrogen oxides contained in the gas. The detection device comprises a treater, a program-controlled current source, a laser, a gas absorption pool, a detector and a signal conditioner. By applying the detection device disclosed by the invention, a high-temperature conversion process is not needed, thus reducing power consumption and energy consumption; and moreover, because the content of the nitrogen oxides in the gas is directly measured, the influence of the existence of other substances on a content detection for the to-be-detected gas is avoided, so that the detection result is more accurate. Furthermore, because a ZrO2 sensor does not need to be used, the problem of poisoning of the ZrO2 sensor due to the compounds of P, S and Si, such as H2S is avoided. Meanwhile, because a ZrO2 sensor technology is a technology monopolized by foreign companies, and the ZrO2 sensor does not need to be used in the detection device disclosed by the invention, the existing technical barrier is broken.