The invention provides an optical fiber axial nondestructive on-line detection device and method, which belong to the technical field of optical fiber device processing and manufacturing, and solve the problem that the fixed axis of a 40-micron ultra-small-diameter polarization maintaining optical fiber is simultaneously suitable for various special optical fibers. The device comprises an image processing device, a rotating part, an optical fiber clamp, an imaging screen, a coherent light emitter and an image recording device. The optical fiber clamp is installed on the rotating part and usedfor clamping an optical fiber, and the rotating part is used for driving the optical fiber to coaxially rotate through the optical fiber clamp. The coherent light emitter and the imaging screen are arranged on the two sides of the optical fiber clamp respectively, and light beams emitted by the coherent light emitter are used for vertically irradiating the optical fiber. A central bright spot filtering part is arranged on the imaging screen; and the image recording device is arranged on one side of the imaging screen towards the optical fiber clamp and is connected with the image processing device. The imaging screen is provided with the central bright spot filtering part, thereby reducing the impact on the imaging quality from the central bright spot, improving the imaging quality, and improving the fixed axis accuracy through the detection device.