Abstract: In order to solve the problem of reduced measurement accuracy caused by zero drift in the online monitoring system for flue gas particles concentration, a zero point automatic calibration system for monitoring the mass concentration of flue gas particles based on laser scattering method was designed. Combining the probability theory in statistics, the influence process of zero drift on measurement accuracy was analyzed, and the system performance was verified through laboratory and on-site experiments. The test results show that the lower the mass concentration of particles, the greater the measurement error caused by zero drift. When the emission concentration of flue gas particles is less than 10 mg / m³, zero drift becomes the main source of error. Zero drift exhibits the characteristics of fluctuating up and down, with a maximum drift value of 2. 02 times the initial value. The online monitoring system for mass concentration of gas particles using zero point automatic calibration achieves a 95% confidence interval half width of 6. 3% in on-site comparative testing. That is, the relative error of 95% of the measured values is less than 6.3%