This paper focuses on the social responsibility of mainstream media microblog in the mobile social era，selects 20 representative microblog accounts as the evaluation objects，evaluates the current situation of social responsibility performance of mainstream media microblog in 2020，and discusses the future development of mainstream media microblog based on the current media ecology and the era mission of mainstream media. On the whole，the current mainstream media microblog in China can better fulfill its social responsibility in communication activities，especially a few head media microblogs play an important role in demonstration and guidance，but the existing problems can not be underestimated. Some media microblogs lack the constructive news idea of problem orientation in news reports，science communication lacks the media consciousness of scientific value guidance，and the coordination of communication and value guidance fails to produce the ideal communication effect. A few media microblogs become the disseminator and producer of false news because they ignore the verification and verification. In the face of the discourse competition in the news field，the community conflict under the circle communication mechanism，the irrational spread under the relationship empowerment，and the loss of trust in the post epidemic era，the mainstream media microblog needs to rethink its own functional value and responsibility，become the authoritative interpreter of hot topics，the active actor of trust reconstruction，and the practice pioneer of Constructive News concept. Mainstream media microblog should play a greater role in the process of social governance.