To detect the changes of vascular smooth muscle Ca²⁺ sensitivity and the expression of its regulatory pathway RhoA-ROCK in different parts of the body under weightlessness, and the effect of tetramethylpyrazine on it.Tail-suspension was used to simulate weightlessness in rats, and the common carotid and superior mesenteric arteries were selected from the anterior and posterior body, respectively. In the common carotid artery of simulated weightlessness rats, the vasoconstriction induced by PHE and KCl was enhanced. The Ca²⁺ sensitivity, the protein expression level of ROCK Ⅱ, the phosphorylation level of MYPT1 and MLC, was increased.After incubating Y-27632 (Specific inhibitor of ROCK)with the common carotid artery of simulated weightlessness rats, the above enhanced changes could be reduced. Administration of tetramethylpyrazine to simulated weightlessness rats could also reduce the above enhanced changes. In the superior mesenteric artery of simulated weightlessness rats, the vasoconstriction, the Ca²⁺ sensitivity, the protein expression level of ROCK Ⅱ, the phosphorylation level of MYPT1 and MLC, was decreased. Incubating Y-27632 with the superior mesenteric artery of simulated weightlessness rats had no effect on the above weakened changes. Administration of tetramethylpyrazine to simulated weightlessness rats also had no effect on the above weakened changes. The results indicate that the distinct changes in Ca²⁺ sensitivity regulated by RhoA-ROCK may be responsible for the different directional changes of vascular contraction function in the anterior and posterior body under weightlessness.Tetramethylpyrazine can inhibit the expression of ROCK to suppress the elevated vascular smooth muscle Ca²⁺ sensitivity, thereby correct the enhanced vascular contraction function in the anterior part of the body under weightlessness, but has no improvement effect on the weakened vascular contraction function in the posterior part of the body under weightlessness.