A computer data transmission system includes a CPU, a photoelectrical conversion module electrically connected to the CPU, a plurality of I/O interface cards, and a plurality of first optical fibers. The photoelectrical conversion module includes a plurality of photoelectrical conversion units. Each I/O interface card includes at least one photoelectrical conversion unit for converting electrical signals to optical signals or converting optical signals to electrical signals. The first optical fibers connect the photoelectrical conversion units of the I/O interface cards and the photoelectrical conversion units of the photoelectrical conversion module. The photoelectrical conversion unit of the photoelectrical conversion module receives electrical signals outputted by the CPU, and convert the electrical signals to optical signals. The converted optical signals are transmitted to the photoelectrical conversion unit of the I/O interface card, and the photoelectrical conversion unit of the I/O interface card converts the optical signals to electrical signals.