Based on the single period dynamics of optically injected semiconductor laser, the generation of photonic microwave and its linewidth narrowing effect by introducing optical feedback are experimentally demonstrated. The experimental results show that the photonic microwave frequency can be continuously and widely tuned in a range of several ten GHz by adjusting the injection parameters. By introducing an optical feedback and properly adjusting the feedback strength, the photonic microwave linewidth is reduced by about two orders of magnitude from a range of 40-100 MHz to a range of 300-900 kHz. The influence of optical feedback length on the microwave linewidth is not obvious except that the photonic microwave frequency exhibits an periodical variation in a small range when the feedback length is finely varied in a small range.