To investigate people's development in an all-round way in an open society, it needs to probe into the theory premise and realistic premise of realizing people's development in an all-round way. The theory premise and realistic premise of people's development in an all-round way embody respectively:that existence of people strengthens day by day, responsibility of people is foregrounded day by day, essentials of people enriched day by day; that people's need types are defined,people's dignity is established, the need of various kinds of people's is met rationally. People's development in an all-round way in an open society is the complicity and entity of this theory premise and realistic premise.