In this paper, we propose an auto-decision system KMCD, which helps remote students choose their majors. The system is based on knowledge of students who want to choose majors and students who have finished their studies. KMCD is a first-order reasoning system equipped with an uncertain reasoning function. A description of KMCD is given in details. The whole decision procedure is comprehensively discussed, which shows the effectiveness and the reasonableness of the system. Examples in the paper illustrate how KMCD can help remote students make their decisions in major-choosing.