Large and rapid variability is one of the defining properties of BL Lac objects. Variability in BL Lac objects has always served as a powerful and important tool for inquring into the physics of these unusual objects. From an extensive seach in the literature we have collected a total of data points of effective observations of BL Lac object S5 0716+714 in V, R and I bands from 1994 to 2008. Then these data are processed on 30 days baseline by autoregressive bispectrum model. In order to eliminate noise interference to extract useful information in the background of Gaussian noise, we propose a method of signal analysis and processing,which analyzes the additive Gaussion noise signal based on autoregressive bispectrum model. Bispectrum is not sensitive to Gaussian noise, it not only suppresses the Gaussion noise in the signal and greatly improves the signal to noise ratio, but also can identify the periodical variations of BL Lac objects. Our results show that the long term periods of variation are 3.33 years and 3.47 years. The conclusion is consistent with 3.3 years period which was found by Raiteri et al. The brightness peak was observed in 2007, so we expect the next burst in 2011—2012.