A photoelectric blackboard pen includes a pen tube, a photoelectric element, a spring, and a spherical lens. The pen tube includes an upper portion and a lower portion away from the upper portion. The lower portion defines a circular through hole. The photoelectric element is positioned on an internal sidewall of the upper portion. The diameter of the spherical lens is slightly larger than that of the through hole. The spherical lens is rotatably positioned in the through hole and partially passes through the through hole. One end of the spring is positioned on the internal sidewall of the upper portion. The diameter of the spherical lens is slightly larger than that of the spring, the other end of the spring sleeves around and resists against the spherical lens.