The energy spectra reflect only the partial properties of high energy X-ray objects. While the temporal variability reflects the dynamic properties of high energy X-ray objects. Both the spectrum and the temporal variability need to be considered when constructing the theoretical emission models. It is generally accepted that the rapid variability of X-ray radiation origins in the vicinity of the compact objects, and reveals the physical properties of the compact objects. Thus the temporal variability will give a strong constraint on the emission models. In this paper, we review the temporal analysis technique of the time lag and its newest development, and the observational data, pay most attention to the properties of the temporal variability such as the time/phase lags that hopefully can help us to discriminate between different theoretical models. We also discuss the models developed to account for the basic observational facts.