The invention relates to a device and a method for detecting whether focusing of a tower-type solar power generation system is precise. The device comprises a first detection body and a second detection body, wherein the first detection body has a first plane, a second plane and a third plane which can reflect light rays and allow the light rays to penetrate through, and the first plane, the second plane and the third plane are arranged at 90 degrees and intersect at a point O; and the second detection body has a fourth plane which can reflect light and allow the light to penetrate through, and the fourth plane is obliquely arranged on the front side, away from the point O, of the first detection body. According to the device and the method, the reflection and light transmission principlesof light are fully utilized, the irradiation direction of solar rays is fed back by means of images of the sun, whether focusing of a heliostat is precise or not can be directly judged through judging whether the solar images are aligned with a heat collector of the tower-type solar power generation system, the detection is very intuitive and convenient, the detection time is greatly saved, and the correction efficiency is improved; and the device is simple in structure, low in cost, and convenient to realize large-scale application.