With the development of applications such as the Internet of Things and mobile devices, the demand for image sensors, which is important for information perception, continues to grow. The analog-to-digital converter (ADC) is an important part of the image sensor, which is responsible for converting the detected analog signal into a digital signal. It not only increases the anti-interference ability and improves the performance of the system, but also enables data processing within the chip and improves the system integration. In order to adapt to the development trend of image sensors towards large arrays, high frame rates, low power consumption, and small pixel sizes, ADCs face challenges in terms of speed, power consumption, and area. Several main architectures of ADCs used in image sensors were reviewed in this paper, and the advantages and disadvantages of these architectures were analyzed. Research progress and future development directions were summarized.