When the student population size of a school or college reaches a certain amount or critical value, student groups will occur a qualitative change, this can be seen most clearly occurrence of various incidents is a conspicuous rise within student groups, the type of incidents occurred more is diverse and facing the situation is even more complex. The article attempts to puts forward the critical value of a school entity population size and its impact factors, and states the management strategy after the population size exceeded the critical value from the viewpoints of proportionate relationships of teachers and students.