In the past decade，philanthropic foundations have increasingly played more important roles in the field of social welfare services in China. However，deep understandings about how the foundations operated and meanwhile implemented their own programs are still inadequate. In this article，the author describes and interprets the implementation process of‘GS Project’by C Foundation，and concludes that C Foundation implements its program ambiguously under a Bottom-line. Inspired by Coleman’s Rational Choice Theory and Bourdieu’s Theory of Practice，the author attempts to conceptualize the‘program-implementing field’，and explores the logic of action in this field. Considering its representation forms，existing grounds and affecting factors，the author argues that the ‘ambiguous implementation under a Bottom-line’could be regarded as a mode of philanthropic programs-operation by the Foundations.