Differential optical absorption spectroscopy (DOAS) is a spectroscopic measurement technique that uses the narrow-band absorption characteristics of gas molecules to derive gas concentrations. This paper introduces the basic principles of DOAS, and develops a program in MATLAB to analyze DOAS data for benzene, toluene and xylenes (BTX). Moreover, the hypothetical and retrieved values of BTX concentration are compared, and the effects of the change in the incident light intensity and particle parameters on concentration retrieval are studied. Results show that the retrieved values are consistent with the hypothetical values of the BTX concentration, indicating the accuracy of the BTX-DOAS data processing program. Preconditions that cannot be directly deduced theoretically in DOAS are validated using a numerical simulation.