To study action mechanism and time of administration of indomethacin in SMAO shock rabbits. Method:Thirty-two SMAO shock rabbits were randomly divided into four groups: control group A,indomethacin 5mg/kg I.V. at the occlusion of superior mesenteric artery (group B), indomethacin 5mg/kg L V. immediately after clamp being removed(group C) and the same dose 30min after clamp being removed(group D). Survival rate,hemodynamics, plasma calcium, myocardial calcium, TXB_2 and 6-keto-PGF_1. levels were observed in 4h shock period. Myocardial apecmen were examined with electronic microscope. Result: After indomethacin I.V,the survival rate was higher and bemodynamie better than those of controll. The plasma calcium level remained stable in indomethacin groups. Myocardial calcium content of group B and C was lower than that of group D and A. The TXB_2 and 6-ketoPGF_1. contents were similar in all groups. Under electronic microscope, the damages were slightest in group C and most serious in group D and A among the four groups. Conclusion:Indomethacin has a beneficial effect on the SMAO shock rabbits ,the mechanism of which can be related to improving myocardium contractivity as well as to blocking calcium channel,rather than the action through prostaglandins. The time of administration should be early as possible after shock.