Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere.Their concentrations can be retrieved by a numerical analysis of the atmospheric absorption spectra. But it has been found that DOAS could not gain continuous data under a bad weather condition.Thus it could not fully fit for the demand of the environment monitoring statute.A prediction technology has been developed, based on the stepwise regression analysis method.It is shown that the forecasting data using this method is consistent with the real data after doing a great deal of experiments. This technology has been used in practice.