The invention discloses a digital double-phase lock-in amplifier for a laser online gas analyzer. The digital double-phase lock-in amplifier comprises an input signal. The input signal inputs signals to phase sensitive detections which are connected with a reference signal. Each phase sensitive detection is connected with a programmable gain amplifier. An input end of each programmable gain amplifier is connected with a bias input. Outputs of programmable gain amplifiers are connected with an ADC (analog to digital converter) conversion module. The digital double-phase lock-in amplifier is simple in structure, and the problems that pure analog phase locking circuits are redundant and complex and digital related calculation of digital phase locking causes large storage and calculation are solved.