Abstract: In order to investigate the swarm parameters of SF₆ alternative gases, a high-precision pulsed Townsend experimental setup was built. With the principle of pulsed Townsend measurements, the swarm parameters, including the effective ionization rate coefficient, electron drift velocity and density-normalized longitudinal diffusion coefficient, could be obtained. The experimental setup and measurement methods were described in detail, as well as the swarm model for signal analysis. The setup and methods were verified with measurement in CO₂ at 10kPa, with the (E/N) range from 0 to 130Td. The present results were compared with experimental reference data, and the swarm parameters calculated by a Boltzmann equation solver. The effective ionization rate coefficient, electron drift velocity and density-normalized longitudinal diffusion coefficient in CO₂ were successfully measured, and the critical electric field strength (E/N)_cr for CO₂ was obtained to be (86±1) Td according to the measured effective ionization rate coefficient. The good agreement was found for the effective ionization rate coefficient between the present data with references. Meanwhile, good agreement could be found when comparing the experimental results with reference data, and the possible error were analyzed. Furthermore, some tests on pure C₄F₇N were done, obtaining its effective ionization rate coefficient at 100 Pa. The experimental apparatus and methods will be used to measure swarm parameters and evaluate the dielectric strength of SF₆ alternative gases, providing significant fundamental data for further study on their discharge mechanism.