The invention discloses preparation method of an automotive cap-shaped beam made of carbon fiber composite materials, and a mold, and aims to solve the problems that in the compression molding of the cap-shaped beam, the strength of different positions is difficult to regulate, and reasonable strength distribution cannot be realized. The preparation method comprises a preparation method of a constant-strength cap-shaped beam, and a preparation method of a variable-strength cap-shaped beam. The preparation method comprises the following steps: laying presoaked cloth which is cut well in a lower concave die (2) according to the number of design layers; placing a flat inflatable bag (3) in the lower concave die (2), enabling the inflatable bag (3) to abut against the presoaked cloth which is put in the lower concave die (2), and laying the presoaked cloth on the upper surface of the inflatable bag (3); dividing a prepared variable-strength cap-shaped beam into n strength sections from right to left, wherein n is not smaller than 2 and not greater than 10; adding different additional materials between layers of the presoaked cloth in each strength section; mounting an upper concave die (1) on the lower concave die (2), and rising the temperature at the same time so as to perform gelation; rising the temperature at the same time so as to perform solidification; removing an air pump; taking down the upper concave die (1) and the inflatable bag (3); and removing burrs of a test beam. The invention further provides the mold.