Abstract: To address the inherent trade-off between timing accuracy and operating power consumption in current real-time clock (RTC) chips, this paper designs an ultra-low-power RTC circuit suitable for low-power systems. The circuit primarily consists of a low-power crystal oscillator circuit, an RC relaxation oscillator circuit, and a distributed clock calibration circuit. Firstly, a low-power crystal oscillator circuit with dynamically adjustable bias current is designed, which disables part of the current mirror branches after the crystal oscillator has fully started up, maintaining stable oscillation with nanoampere-level current. Meanwhile, a distributed low-jitter clock calibration algorithm based on two's complement coding is proposed, which employs a periodically awakened high-precision crystal oscillator clock as a reference to perform periodic frequency calibration on the low-power RC oscillator, supporting flexible configuration of calibration accuracy and range. This approach effectively combines the high-precision characteristic of the crystal oscillator with the low-power advantage of the RC oscillator. Key circuit design, layout generation, and simulation verification are completed based on 55 nm CMOS process. Post-layout simulation results demonstrate that under a 1.8 V supply voltage, the power consumption of the crystal oscillator during the sustaining oscillation phase is 141.3 nW, and in the automatic calibration mode with the crystal oscillator as the reference source and a calibration accuracy set to 2 ppm, the average power consumption is 66.2 nW, achieving synergistic optimization of ultra-low power and high precision.