The dynamic characteristics are investigated for a microring laser with an external radius of 12 μm subject to external optical injection. Single-mode operation with a side mode suppression ratio of 33.4 dB is realized at a biasing current of 25 mA and a temperature of 290 K, and the corresponding small-signal modulation response is obtained with a resonance peak frequency of 7.5 GHz. Under the optical injection from a tunable laser, the improvements of the small-signal modulation response induced by four-wave mixing are observed for the microring laser, which shows an additional resonance peak around the frequency of the beat frequency between the lasing mode and the injecting light. Furthermore, optical generation of a microwave signal is realized by the light beating between the lasing mode and the injecting light measured by a high-speed photodetector and a spectrum analyzer.