Abstract: On the basis of a previous paper of the same title earthquakes of Mge;6 occurred during the period 1970-1980 and two earthquakes of M 7 of the 1960 's on the main land of China, are analysed. It is shown that the conclusions reached about '' background gaps, preparatory gaps and imminent earthquakes in the previous paper have general significance and thus it substantiates the results of the previous paper. The empirical -formula has been recomputed.Three criteria are proposed for the identification of preparatory gaps: 1) Along with the formation of a preparation gap, the seismic strain release should be accelerated in the gap area and its vicinity; 2) The ratio of earthquake frequencyoutside and inside the gap (k=N(out)+1/N(in)+1 ) should reach a maximum value during theprocess of its formation; 3) Some moderate earthquakes in the form of early fore-shocks would occur in the forthcoming epicentral area before the formation of the background gap. Besides, it is found there is a linear relation between Sigma;E1/3 and logarithm of the longer axis of a preparatory gap, where E is the energy release in the preparatory gap and its neighbouring region. The empirical formula obtained can be used as a time criterion of the occurrence of the imminent earthquake. Finally, the physical mechanism of imminent earthquakes and the dimension of the area of preparatory gaps are discussed.