The invention relates to a method for realizing a secondary circuit with dual line protection. An intrinsically separated merging unit and an intelligent terminal are in communication connection witha line protection unit, and a point-to-point connection circuit is formed. The line protection unit, the intrinsically separated merging unit and the intelligent terminal are connected to an intrinsically separated process layer switch through a fiber network to form a network connection circuit. The secondary circuit with dual line protection is formed by two independent connection circuits. Theproblem that a single secondary circuit has many optical fiber fusion nodes and the secondary circuit is easily abnormal to cause frequent power failure maintenance is solved, and therefore, the reliability of the line power supply is effectively improved.