To enhance the automatic detection and tracking capabilities of passive weak targets under low signal-to noise ratios and in the presence of multiple target interference, a novel algorithm with multi-line spectrum fusion and optimal line spectrum target automatic tracking is proposed. This algorithm is based on line spectrum detection and automatically tracks targets with fused multi-line spectrum features, establishing the criteria for the creation, deletion, fusion, and association of line spectrum targets. It employs a Multi-Hypothesis Tracking(MHT) algorithm tailored for trajectories to automatically track multiple targets, offering the advantages of low computational complexity and strong weak target tracking capability. Analysis of sea trial data indicates that even in the presence of strong target interference, this algorithm can still provide stable tracking for weak targets with line spectrum characteristics.