Abstract: As one of the three main tests for spacecraft products, the developmental test is to improve the inherent reliability of the spacecraft products. The more and more stringent requirements for the reliability and the stability of the spacecraft products on orbit make the developmental test more and more important. However, due to the lack of good understanding, the practical test does not perform as expected. With consideration of the current situation and the demand of the developmental test for the spacecraft products, some test concepts of the developmental test are clarified in this paper, including how to carry out the developmental test, and the unique role of the developmental test played in the improvement of the inherent reliability of the spacecraft products based on some typical cases. The paper gives some guidance in how to carrying out the developmental test properly and effectively.