A high precision RC oscillator with chopper topology was designed in a 0.18 μm CMOS process. The structure had a better suppression effect on comparator’s offset, and compensated for the effect of comparator transmission delay on the output clock frequency to achieve better temperature characteristics. At the same time, the use of LDO power supply to the main circuit of the oscillator effectively suppressed the impact of power supply voltage fluctuations on the output frequency. In addition, the oscillator used a capacitive trimming network to reduce the impact of process drift on the center frequency. Simulation results show that the designed oscillator can be trimmed to calibrate the frequency to the nominal value of 2 MHz under different process corners. The fluctuation of the output frequency is only 0.87% in the temperature range of －40 to 125 ℃, and 0.21% in the power supply voltage range of 3 to 6 V. Compared with the same type of on-chip RC oscillator, the proposed circuit’s drift of temperature, supply voltage and process is better suppressed.