To meet the requirement of high-end ultra-precision equipment, such as photolithography machines and ultra-precision CNC machine tools for precise plane positioning, a planar two-dimensional displacement sensor based on multi-frequency magnetic field coupling is proposed. The sensor consists of a fixed length and a moving ruler. The fixed length is composed of a magnetically conductive substrate and an excitation coil in X- and Y-directions, and the moving ruler is composed of a magnetically conductive substrate and an induction coil in X- and Y-directions. By passing sine and cosine excitation signals to the excitation coils in X- and Y- direction, a two-dimensional uniform magnetic field array with multi-frequency magnetic field coupling is established on the fixed scale, and an electrical signal with displacement information is induced by the moving ruler. The feasibility of the multi-frequency magnetic field direct decoupling differential structure and amplitude modulation solution methods are evaluated through theoretical derivation and electromagnetic simulation. The simulation error is analyzed, and the sensor structure is optimized. Finally, the sensor prototype is manufactured by the PCB process and related experimental research is carried out. The experimental results show that the sensor can accurately measure the two-dimensional displacement in the measuring range of 150 mm × 150 mm. The measurement accuracy of the X-direction is ± 33. 08 μm and the measurement accuracy in the Y-direction is ± 36. 95 μm. The peak-to-peak values of the original internal displacement errors in the X and Y directions of the optimized sensor prototype are reduced by 49. 1% and 50. 7% on the original basis.