We report a single-frequency, narrow-linewidth semiconductor pulsed laser based on pump current modulation and optical injection locking technique. A homemade monolithic non-planar ring oscillator laser is employed as the seed to guarantee the single-frequency narrow-linewidth performance. Simultaneously, pulse operation is achieved by directly modulating the pump current of the semiconductor laser. The single-frequency pulsed laser has achieved a pulse repetition rate of 50 kHz-1 MHz, a pulse duration ranging from 120 ns to a quasi-continuous state, and a peak power of 160 mW. Moreover, the SFPL has reached a carrier linewidth as narrow as 905 ± 16 Hz, optical spectrum signal-to-noise ratio of better than 70 dB at a center wavelength of 1064.45 nm. Such extremely narrow-linewidth, repetition-rate and pulse-width tunable single-frequency pulsed laser has great potential for applications in coherent LIDAR, metrology, remote sensing, and nonlinear frequency conversion.