The invention discloses an infrared-visible light dual-band photoelectric detection system and an axis angle error measuring method. The Infrared-visible light dual-band photoelectric detection systemand axis angle error measuring method comprises a reflecting system, a beam splitter, a visible light imaging unit on a reflecting path of the beam splitter, a medium-wave infrared imaging unit on atransmitting path, and an axis angle error measuring unit. The axis angle error measuring method comprises: I, initializing a CCD (charge coupled device) sensor, and acquiring a background gray image;II, centering a medium-wave infrared axis; III, performing visible light spot imaging; IV, acquiring a visible light spot image; V, acquiring coordinates of a center of mass of the visible light spotimage; VI, calculating axis angle error. The infrared-visible light dual-band photoelectric detection system and the axis angle error measuring method have the advantages that the advantages of a visible light band optical system and those of a medium-wave infrared band optical system are combined, observing efficiency and inspecting efficiency are improved, remote high-definition all-weather imaging is achieved, imaging quality is effectively improved, the axis angle error measuring unit can measure angle errors for visible light axis and medium-wave infrared axis, and stability of the photoelectric detection system can be measured.