Abstract:Kant's "critique of reason" is a question on reason, which was based on natural sciences, such as mathematics, physics etc, and it pursued the premise and condition of natural sciences, which led to the conclusion: understanding has built the world's order. This conclusion lacked the root for culture. Cassirer considers that, myths, language, art, religion, etc are all spiritual forms of human being, and that his cultural criticism, covering both natural sciences and social sciences, from the angle of the theory of function, broke through Kant's narrow starting point and managed to find out the criterion and foundation on which the whole culture were to be constructed, namely the cultural root.