Poor bonding occurs with resin due to surface inertness of carbon fiber (CF), so CF surfaces were often treated. In some common surface treatments, sizing was a simple and effective modification method. Polyurethane (PU) was used as the main component of sizing agents due to its similar structure to polyamide 6 (PA6). The CF/PA6 composites’ interfacial properties were improved using PU as a sizing agent. Meanwhile, in this paper, glycidol (GLD) was introduced into the PU emulsion so that the epoxy group reacted with the carboxyl group on the acidified CF. After testing, when the content of glycidyl in the sizing agent is 2%, the CF/PA6 composites showed an important improvement in tensile, impact, and flexural strengths, which increased by 49.4%, 94.6%, and 53.2%, respectively. In addition, the effect of modified WPU sizing agents with different GLD contents on the properties of CF/PA6 composites was investigated.