Abstract: With the rapid development of smart phone and mobile Internet,the life style of people is changing．At present,the smart phone terminal integrates different sensors,such as GPS,Wi-Fi,camera,microphone,and so on．By analyzing the information collected from mobile phone sensing,it can help understand and identify users’ activities and provide personalized activity recommendation service．This paper mainly focused on improving the life in big communities (such as in a university campus).We put forward a social activity recommendation system based on background sound recognition using mobile phones．The system,named Mobile Sound Sensing and Activity Recommender (MSSAR),can gather the background sounds through the embedded microphone of mobile phones,recognizing the ongoing user activities (such as in the coffee shop,in a meeting)．Furthermore,based on the online interactive historical data,MSSAR can calculate the intimacy among friends and suggest activities accordingly．This system has positive effects to enhance social connection among users and promote communication in the community.

Key words: Smart phone,Mobile internet,Background recognition,Association with online and offline,Social activity recommendation