With the rapid development of mobile information technology and social media networks, it is feasible for college English teachers to get access to social networks such as QQ, Email and MSN as a way of practicing English writing beyond classroom. Similarly, it is also possible for teachers to utilize WeChat Platform where online communities for students and teachers can be established to combine collaborative and mobile learning together as a complementary way of classroom writing teaching. WeChat Platform, as the most popular software in China, owns the advantages of transmitting instant message, videos and pictures, which supplies students more chances to collaborate and interact with each other/one another at different stages of writing tasks. This research explores the application collaborative learning of college English writing on WeChat Platform. Based on the one-semester research as well as the questionnaire of the pre-test and post-test, it is revealed that, although there are still a few challenges for students and teachers to face, this mode of college English writing contributes to cultivating the students' team spirit, enhancing their initiative, improving their writing efficiency and developing their critical thinking by engaging in student-student and student-teacher collaboration and interaction, information sharing, communicating and socializing with classmates.