The invention relates to a distributed optical fiber pipeline safety advance warning system based on phase interference. After passing through an optoisolator [17], a laser is divided into two bunches by an optical fiber coupler [15], and then passes through polarization state controllers [13a] and [13b], output and is connected with guide optical fibers [3a] and [4a] through ports [3] and [4], the guide optical fiber [3a] is connected with a fiber core [3b], the guide optical fiber [4a] is connected with fiber cores [7] and [8] after passing through a head end box [11], and the fiber cores [3b], [7] and [8] are connected with a terminal box [10]; fiber cores [1b] and [2b] which are led out of the terminal box [10] are respectively connected with guide optical fibers [1a] and [2a], respectively and sequentially connected with photodetectors [12a] and [12b] and signal conditioning units [14a] and [14b] through ports [1] and [2], and connected with a signal processing computer [18] after being differentially input into an analog-to-digital converter [16a] together; the fiber cores [7] and [8] which are led out of the terminal box [10] are connected to the head end box [11], respectively connected with photodetectors [12c] and [12d] by guide optical fibers [5a] and [6a] and ports [5] and [6], and are differentially input into an analog-to-digital converter [16b] together after the outputs are respectively connected with signal conditioning units [14c] and [14d], and the output of the analog-to-digital converter [16b] is connected with a signal processing computer [19].