In response to the demand for precision linear displacement measurement in fields such as precision manufacturing, aerospace industry, and military applications, an absolute linear time-grating displacement sensor based on secondary coupling is proposed. The fixed scale employs a discretely distributed passive design, which avoids the distributed inductance and capacitance caused by interlayer connection through-holes in traditional designs, thereby improving the continuity and uniformity of the induced magnetic field. Both excitation and sensing signal processing are concentrated on the slider side, requiring only the arrangement of leads on the slider side, with magnetic coupling confined to the excitation coil area. This design effectively suppresses interference from electromagnetic coupling between uncovered coils on the stator and ambient electromagnetic waves, while expanding the sensor′s application scope. First, a planar transient magnetic field coupling model is established, and a dual-array absolute sensor measurement model with its sensing mechanism is constructed. By using a coprime pole-number absolute displacement calculation scheme, the allowable error range in absolute displacement measurement is expanded, and the accuracy of absolute displacement calculation is improved. Additionally, a novel same-frequency modulation signal decoupling method is proposed, which achieves a high signal-to-noise ratio while significantly reducing ADC sampling rate requirements by optimizing the signal processing mechanism, thus resolving the contradiction between ADC sampling rate and resolution. Through electromagnetic finite element simulation, theoretical verification and error analysis of the sensor are conducted, determining the optimal installation gap to be 0.5 mm. Finally, sensor prototypes are fabricated using PCB technology, and experimental studies are performed. The experimental results show that the proposed sensor can achieve absolute displacement measurement within a range of 203 mm, with original measurement errors ranging from -12.62 to +3.23 μm.