It is found that two reflected walls of fiber micro-cavity fabricated by one-step femtosecond laser micro-machining technology are not perpendicular to the fiber axis. The cavity shape is decided by the relative position of focused femtosecond laser and fiber, which can be approximated as V-shaped when femtosecond laser is focused on the side surface of the fiber. Compared with conventional fiber Fabry-Pérot (F-P) cavity, the free spectral range, optical loss and the interference fringe of the V-shaped fiber F-P cavity contrast change with the wavelength, showing abnormal characteristics. By introducing the concept of inclination factor, V-shaped fiber micro-cavity model is constructed, the cavity interference formula and the V-shaped micro-cavity interference theory are established. According to this theory, the effect of reflector inclination degree on interferogram characteristics of V-shaped F-P micro-cavity is simulated. The simulated interferogram is verified by experimental results.