In order to explore the influence of coaxial cable shielding influencing factors on its shielding effectiveness （SE）， a test set was built based on the shielding attenuation triaxial method to evaluate the SE of coaxial cables and connectors for in-vehicle communication. The effect of the shielding layer， end connector， and segmentation on the SE of coaxial cable was investigated， and the SE test data in the range of 0.1 MHz to 3 GHz was obtained. The analysis results show that for the vehicle communication coaxial cable RG174 series， the double shielding layer is 10~15 dB higher than the SE of the single shielding layer.The cable segmentation and end connector can all reduce their SE. The SE of the cable with the end connector and segmentation is more obvious， and the drop can reach 10 dB.Moreover， the end connector changes the cutoff frequency of the cable. The research results can be used to guide the selection and segment layout design of coaxial cables for in-vehicle communication and solve electromagnetic compatibility problems such as electromagnetic emission and interference of in-vehicle communication equipment in the coaxial cable and their connection parts.