Budget constraints always play a critical role in the customer’s purchasing decisions． The literature has disproportionately focused on how firms induce customer valuation while remaining silent on the influence of consumers’budget constraint and on how firm’s marketing strategy should adjust in the presence of budget constraints． The paper studies these questions in the context of Ｒeferral Ｒeward Program ( ＲＲP ) ． A stylized model consisting of three players is built: A firm，an existing customer，and a potential customer． The budget constraint is the potential customer’s private information． The paper finds that the policy of high price and high referral reward is not always effective and there exists one ＲＲP optimal policy for the firm when the potential customer has less budget pressure and medium valuation． Furthermore，ＲＲP might be optimal whether the po-tential customer is with low-or high-valuation，but works of ＲＲP is in completely different manners． Our analy-sis is also extended to consider firm financing and customers’aversion toward paid referral．