This paper presents the consumer’s “economic rationality”, adopting rich connotation of economic sociology when he makes its utility maximization choice for financial services. The principal-agent relationship between the private banks and the customer is co-constructed by the formal contract and implicit contract such as trust mechanism. Chinese private banks are confronting problem of the scale expansion and poor earnings. How to meet the high net worth clients “personalized” requirement is the key to solve the problems. Analysis shows that Chinese special trust mechanism such as familism, social network, “rule by man”, system defect contributed to the Chinese high net worth individuals for property inheritance demand, social relations needs, financing needs, preferences to speculation and security needs. For the future development of Chinese private banks, system cultivation and trust cultivation is worthy of consideration, but the pressing demand for the private bank is to strengthen the risk management to control the risk of product not to transfer into the reputation risk.