Abstract: Objective: To approach the early diagnosis value of CT and MRI for acute cerebral infarction,and compare the difference of curative effect of urokinase thrombolysis between different time window.Methods: We reviewed the diagnose time by CT and MRI of 100 cases of acute cerebral infarction,and treated by short period intravenous urokinase thromblytic therapy in two different time window groups,50 cases in each,<3 hours group and 3-12 hours group,and compared diagnosic method and curative effect.Results: The confirmed diagnosis time of MRI was obriously sherter than that of CT(P<0.01),whereas difference of 1.5T MRI and 3.0T MRI had no statistic meaning(P>0.05).The focus numbers found by CT,1.5T MRI 3.0T MRI had statistic sense(P<0.01),3.0T MRI was the most.The grade of neuro function defection after 14 days of <3 hours thromblysis group was lower than the grade of 3-12 hours group(P<0.001).The effectivity of <3 hours group was 88%,which was higher than 3-12 hours group(66%).Conclusions: Acute cerebral infarction could be diagnosed early by MRI,high field MRI(3.0T) could show more focus number;Urokinase thromblytic therapy is safe and effective,and the earlier the better.