We report a time-gated fluorescence lifetime imaging microscopy (FLIM) using an active timing-controlled device and an ultrafast picosecond diode laser. This system could utilize more precise synchronization between laser excitation pulse and ICCD gate combining low timing-jitter diode laser with high precise timing control unit. Two flexible trigger signals for laser source and intensifier gate could adjust time sequence with picosecond precision compared with conventional passive delay adjustment. The importance of the adjustable repetition rate of this laser source is discussed with respect to noise reduction and precision in the lifetime determination, illustrating a further significant advantage over conventional mode-locked solid-state lasers. This FLIM system instrument could satisfy a wide temporal dynamic range demand for various biological applications.