The humanistic reason in the Western Zhou civilization is the foundation of Chinese humanistic spirit. Being affected by anti-religious ideology in the 20th century, it was considered as a reaction against religion by academia in the past years. Nevertheless, the author believes that the Chinese civilization before the Axial Age was still in the religious period, and the changes in late Shang and Western Zhou did not eliminate religion. Actually, those changes can be considered as a revolutionary transformation of natural religion in Shang dynasty and a new creation of ethical religion, which bred the humanistic spirit of Western Zhou and produced a new supreme god (Heaven) as well as developed a new interpretation of Heaven’s will—matching one’s virtue with that of Heaven. Besides, a new way connecting human with Heaven was created and thus the bond between Heaven and human got strengthened with the influence of moral providence got broadened. The birth of humanistic spirit in Western Zhou was not only the attenuation of traditional natural religion but also the fruit of the development of new ethical religion. The key to understanding the civilization of Western Zhou lies in the comprehension of the endogenous relation between new ethical religion and humanistic reason.