The invention provides pixel circuit and a control method thereof and a global contrast detection image sensor. The pixel circuit comprises, sequentially connected, a photosensitive circuit, a contrast detection circuit and a reading circuit. and the photosensitive circuit, the contrast detection circuit and the reading circuit are sequentially connected, wherein the photosensitive circuit is used for exposure to generate photoelectric current, and outputs voltage signal in proportional to the logarithm of the photoelectric current to the contrast detection circuit, the contrast detection circuit amplifies the voltage signal, obtains contrasting signal of the light intensity according to the change of the voltage signal, and outputs the contrasting signal to the reading circuit, and the read circuit stores the contrasting signal and outputs contrasting signal to a column data line. The contrasting signal of the light intensity can be obtained directly in the pixel circuit, The image sensor sequentially outputs and records the contrasting signals, and operation consumption and system power consumption during subsequent image processing are eliminated. The application of contrast analysis is faster and timely.