To enhance sensor resolution and accuracy without increasing size, while enabling absolute angular displacement measurement for space-constrained industrial applications, this paper proposes a high-resolution absolute time grating angular displacement sensor using secondary modulation dual-channel synchronization. The sensor consists of a fixed ruler, a moving ruler, and a driving circuit board. The fixed ruler includes two fine machine code channel excitation coils, two coarse machine code channel induction coils, and the secondary winding of an electromagnetic coupling coil. The moving ruler has two fine machine code channel induction coils, two coarse machine code channel excitation coils, and the primary winding of the electromagnetic coupling coil. The driving circuit board contains a driving signal generator, two induction signal processors, and an FPGA core circuit. The fine machine code channel induction coils on the moving ruler are connected in series with the coarse machine code channel excitation coils for secondary modulation. When the fine machine code channel excitation coil is powered, the angular displacement signals from the fine machine code channel induction coils are modulated onto the coarse machine code channel, enhancing resolution by effectively integrating both channels. Additionally, one precision machine′s induction signal is transmitted back to the fixed ruler via the electromagnetic coupling coil as a full-cycle positioning signal. Both signals are processed synchronously by the FPGA for absolute angular displacement measurement. A prototype with an outer diameter of 140 mm was fabricated using PCB technology. Experiments show that the sensor achieves absolute angular displacement measurement with a single drive circuit, improving resolution from 0.38″ to 0.2″ (a 47% increase) and reducing measurement error from ±34.14″ to ±16.06″ (a 53% reduces).