The evolution of internet public opinion is usually divided into three stages: the germination stage, the pervasion stage and the attenuation stage. This article attempts to analyze the evolution of internet public opinion from the perspective of social psychology. The germination of internet public opinion is largely derived from the stimulation of the current social mentality which includes the growing social sense of unfairness, deprivation feelings towards the power and the rich, diversified values and the reducing social identity, various forms of irrational mentality, the lack of faith and social crisis of confidence, etc. During the pervasion stage, many kinds of internet users' mentality (conformist mentality, reversal mentality and transference mentality) affect the balance within the "public opinion field". Subsequently, the transfer of internet users' "attention" prompts the internet public opinion attenuation gradually. <<