Abstract: At present, the formula method is commonly used to calculate the VOCs emission from the tank farm, but the results varies greatly with the values of the calculation parameters adopted. In order to more accurately capture the VOCs emission data from the tank farm, the VOCs emission monitoring technology for tank farm was studied based on the Open Path Fourier Transform Infrared Spectrometry (OP-FTIR) field measurement method. An independent tank farm composed of 4 tanks in one petrochemical enterprise was taken as the research object, the VOCs volume fraction and meteorological data of a total of 7 light paths around the tank farm and within the tank farm space were continuously acquired based on OP-FTIR field measurement method, and the VOCs emission was calculated by mass flux method. The results show that the average volume fraction of VOCs emitted from the tank farm is 59.8×10^－9, and the emission is 48.21 t/a (calculated as 8 760 hours per year). This technology provides a new method for scientific calculation of VOCs emission from tank farm.