There is an informal contractual arrangement behind the attribution of higher education investment income. Educees ex- change their social income that should be distributed with the direct economic income that should be distributed by the public subject. The direct economic income is ultimately all private and private income can be amplified through exchange. This exchange mechanism is determined by the particularity of higher education income,and is modified afterwards through signal transmission mechanism,game mechanism,incentive and penalty mechanism. A fair system of cost-sharing,improving the quality of higher education,promoting the orderly competition of higher education,and charging according to school level are essential to the stability and equilibrium of the pri- vate rate of return of higher education. They are important foundations for the long-term survival of informal contracts and the sustain- able development of higher education.