The invention discloses a TDLAS based escaped ammonia concentration detection device and method. The device comprises a microprocessor, a current control circuit, a temperature control circuit, a feedback control circuit, a laser, a collimator, an optical gas chamber, a photoelectric detector, a data processing circuit and a display circuit, wherein the output ends of the current control circuit and the temperature control circuit are connected with the input end of the laser, the output end of the photoelectric detector is connected with the output end of a pre-amplification circuit, and the output end of the microprocessor is connected with the input ends of the current control circuit, the temperature control circuit and the feedback control circuit. According to the invention, the absorption peak position of ammonia gas can be locked accurately and quickly without a reference gas chamber, so that the development cost of an escaped ammonia monitoring device is saved, optical noise generated when light rays pass through an optical fiber splitter can be avoided, the signal to noise ratio of a system is improved, and the accuracy of an escaped ammonia concentration detection result can be improved greatly.