The Taiji program is focused on achieving space-based gravitational wave detection in the frequency range of 0.1 mHz–1 Hz. To achieve drag-free control, Taiji satellites must be equipped with micro-thrusters that satisfy stringent requirements, including a continuously adjustable thrust, thrust resolution of 0.1 µN, thrust noise of 0.1 μN∙Hz^−0.5 and response time of less than 100 ms. This paper presents the progress of a variable cold gas micro-thruster being developed for the Taiji program. A series of technologies such as a bidirectional piezoelectric drive, spherical valve core, conical nozzle seal, miniature gas chamber, high thruster integration, combined digital and analogue communication and high-frequency closed-loop thrust control were employed to achieve engineering prototypes of a low-noise and fast-response micro-thruster. Ground performance tests indicate that the micro-thruster achieved a minimum thrust of close to 1.1 nN, a thrust resolution of 0.05 μN and a maximum specific impulse of 69.1 s using nitrogen gas as the working fluid. The thrust noise was less than 0.1 μN∙Hz^−0.5 in the frequency band of 10 mHz–1 Hz, and the thrust response time was 140 ms. The control parameters were further optimised to achieve a flow response time of 50 ms. The results indicate that the developed micro-thruster essentially met the performance requirements for drag-free control to facilitate space-based gravitational wave detection.