Abstract: To investigate the in vitro release, in vivo pharmacokinetics, and the in vitro-in vivo correlation of progesterone suspension injection, self-made progesterone suspension injection was taken as an example. The in vitro release curves of three different particle sizes of progesterone suspension injections were measured using paddle method and dialysis bag method. The in vivo pharmacokinetic characteristics of self-made progesterone suspension injection was studied on SD rats. The plasma concentration of self-made progesterone preparation was detected after intramuscular injection, and correlated with the in vitro release profiles obtained by the dialysis bag method after processing by Wagner-Nelson method. The results showed that when the in vitro release of three different particle sizes of progesterone suspension injections was measured by the paddle method, more than 85% was rapidly released within 20 min, while 85% cumulative release was reached at 40 h, 84 h and 120 h by dialysis bag method, respectively. The release rate obtained by the dialysis bag method was basically consistent with the in vivo release trend, with a correlation coefficient of >0.95, indicating a strong in vivo and in vitro correlation. This study provides some reference for the establishment of the in vitro and in vivo correlation of long-acting suspension injection.