Based on the photoelectric principle, an accurate method to measure the deep hole straightness is built according to the changing rule of the output voltage. The changing rule of the actual hole center is analyzed when the photodetector has translational and rotational movements. Based on the least squares principle，the relationship between the deep hole straightness and the output voltage is deduced, which provides the theoretical foundation for deep hole straightness photoelectric measurement. According to the photoelectric measurement theory, a self-positioning, real-time display device of deep hole straightness measurement deviation is designed, which can effectively achieve automatic and non-destructive detection of deep hole straightness measurement.