On the basis of statistical distribution and information entropy theory, information entropy of magnitude (Hm)and information entropy of interval time (Ht)are defined, and their formulas are derived. By means of specio-temporal scanning and calculating, Hm and Ht appear low-value anomaly in 13 years before strong earthquake. Having the better correlation with earthquakes, the Hm and Ht can be used as earthquake forecast indexes for mid or mid -short term.