At present, China's aerospace product development mission are characterized by mammoth task and high responsibility, in which situation, the role of knowledge in business process is particularly prominent. Although we have realized the importance of the problem, and embarked on the accumulation job, the problem faced is that we lack the criteria to judge our harvest, which spontaneously caused that we cannot define the quality and practical value of accumulated knowledge. Focusing of above problems, the paper puts forward a knowledge maturity model for aerospace product development, which divides knowledge maturity into 6 levels according to development process. Criteria of each level as well as translation condition to next grade is elaborated, assessment note is specially stated, aiming at offering enterprises a potent method for knowledge system construction and evaluation.