Mass-Emergency (ME), especially negative ME as a kind of sociological phenomenon, attracted attentions of many researchers in sociology, crisis management and psychology. The evolution of ME corresponded with inter-group emotions intensity closely. But previous researches paid little attentions to measure intra-group emotions intensity, let alone the evolution mechanism of it, as a result, people know little about how intra-group emotions intensity varied with time, and then there is no way to monitor the variation trend of it,which is a bad news to the ME-prevention. Most former researches focused on the micro perspective of emotion intensity, or to say, on individual emotion intensity when inter-group emotion transmitted, not on the intra-group emotion intensity of the whole group. Thus their results had a lot of limitations, and always fit the reality bad. In order to improve ecological validity of model which described the transformation law of intra-group emotions intensity, this study adopted 3 kinds of methods, including mathematical modeling, computer simulation and psychological empirical research. In one aspect, mathematical modeling, computer simulation contribute to reveal the law of intra-group emotion intensity changed with time (system of dynamic law). Firstly, The present study defined an inter-group-psychological variable which described emotion intensity of whole groups when inter-group emotion transmitted. And at the same time, a model was built to describe and explored dynamic mechanism of intra-group emotion intensity which consisted of spreaders and stiflers. Besides, sense of group identity was considered into the model, and the model concluded several parameters:Ta(t)indicated the rate of emotion intensity which was above a(a=1,2,3,4,5)1 mean the lowest, 5 mean the highest.Ea indicated the lowest sense of identity level of emotion intensity ”a”.ω indicated unknown parameter.ω1and ω2 indicated rate of spreader and stifler at any point in time. Secondly, this study tested basic hypothesis and ecological validity of the model. In four experiment condition: iner-group positive emotion, iner-group negative emotion, out-group positive emotion and out-group negative emotion. The experiment was conducted in a computer lab, participants were recruited from 20 classes, amount to 686 college students, 3 participants of each class were randomly selected, MP3 material which was used to trigger emotions and was presented to the 3 participants, after the presentation, they can choose to transmit the MP3 to other participants or not, and then report back their choices to experimenter. In the meanwhile, they should also report their emotion intensity after heard that MP3 material, on papers. At last, the intra-group emotion intensity of every time point was calculated, and the result was compared to computer simulation data. Results showed that (1) Model of this study fit the empirical data good, which mean that the model had good ecological validity. The system of dynamic mechanism of intra-group emotion intensity could be described by spreaders, stiflers and group identifications. (2) During the emotion transmission, both the portion of spreaders and inter-group emotion intensity is first rising and then descending as time goes by. But this study found that Compared to the climax time of spreader, intra-group emotion intensity is delayed.