This study focuses on the processing of prepregs and the mechanical properties of composites prepared using the prepregs, revealing certain crucial process requirements. To the best of our knowledge, studies correlating the prepreg manufacturing process and the mechanical properties of composites prepared using the prepregs have not been reported. Normally, carbon fiber reinforced thermoplastic (CFRTP) is prepared using the resin film infusion process. However, we used the melt impregnation method to manufacture unidirectional polypropylene prepregs to achieve efficient impregnation of carbon fiber bundles. This method merely requires an extruder to infuse the melt resin, making it possible to control different degrees of acid modification of polypropylene and the process temperature to investigate the composite properties. As a result, we could optimize the process parameters and the temperature conditions to manufacture unidirectional carbon fiber prepregs and successfully prepare good composite laminates with excellent carbon fiber distribution and low void content (below 1.0%).