Disclosed are a manufacturing method for a support substrate (14), and an LED display device. The support substrate (14) is made of a carbon fiber material. The manufacturing method for the support substrate (14) comprises the steps of: S1: preparing a carbon fiber prepreg fabric; S2: preparing a support substrate (14) sheet; S3: pre-forming; and S4: molding. The LED display device comprises at least one cellular LED display screen (1), and the cellular LED display screen (1) comprises a support substrate (14) manufactured using the abovementioned method. The cellular LED display screen (1) comprises an LED display module, the support substrate (14), a control plate and a back cover (16). The LED display module comprises a face guard (11), a lamp plate (12) and a backing plate (13). The support substrate (14) is arranged between the LED display module and the control plate in a sandwich manner; the back cover (16) is connected to the support substrate (14) through studs; and the adjacent cellular LED display screens (1) are assembled by connecting bases (142) and locating pins (143) arranged at the four corners of the support substrate (14). The LED display device is simple in structure, light and thin, has a strong bearing capacity, and is convenient to install and low in transportation costs.