To effectively eliminate the influence of interference signals in CMOS technology’s photosensitive and signal processing circuits and achieve high-precision angle position measurement, a coarse and fine combination optoelectronic angle position coding circuit with adaptive threshold was designed. A study was conducted on the adaptive threshold circuit of a trans-impedance amplifier and the coarse and fine data combination circuit. Firstly, the coarse channel adopts a 1-bit comparison circuit to achieve high-speed conversion, and half of the voltage signal generated by the photodiode is used as the comparison voltage to achieve an adaptive voltage threshold. Secondly, the precision channel adopts a tracking conversion method to automatically track the optoelectronic signals of the sine and cosine transformations of the master channel, achieving a 9-bit angle position data of precision channel encoding. Finally, the combination of coarse and fine tracks encoded data signals is controlled by the highest bit of the precision channel data, achieving an 18 data conversion. A constant LED light intensity circuit was designed, utilizing the sine and cosine voltage signals generated by precision channel photodiodes. Design a square sum circuit of sine and cosine currents to achieve LED’s constant illumination intensity, eliminating the influence of temperature changes on LED brightness. The chip is fabricated using a 0.35 μm CMOS process, with a 3.1 × 5.4 mm chip size. The test results show that the conversion accuracy reaches ± 15ʺ. The circuit meets the requirements of a high-precision Φ58 mm absolute position optoelectronic encoder.