When outdoor installation line protection devices communicate with other devices in the plug-and-play smart substation, transmitting single-mode and multi-mode optical signals should be at the same optical interface, and then a high-density prefabricated dual-mode (single-mode and multi-mode) optical cable with reliable performance and fast connection is designed. The prefabricated optical cable can be used in harsh weather for a long period. The optical fiber connector has the characteristics of low insertion loss and high return loss. This prefabricated optical cable overcomes the problems of single optical transmission and unreliable performance of existing prefabricated fiber optic cable, and improves the efficiency and reliability of optical connection. The test and verification of the dual-mode prefabricated optical cable show that it has excellent performance and achieves the expected goal. The work is supported by Science and Technology Project of State Grid Hubei Electric Power Company (No. HB1702-0348).