Objective: It is one of the hotspot researches on cerebrovascular disease to study the onset and recovery mechanism of aphasia for providing theoretical evidence in the rehabilitation of aphasia patients. Data sources: With computer, a MEDLINE search of English-language articles published from January 1980 to January 2004 was performed using the searching terms "aphasia, recovery", "aphasia, hypoperfusion", "aphasia, metabolic", "lateralization, language". Meanwhile, the compute search of Chinese-language articles published in Wanfang database between January 2002 to October 2004 was also performed by using the term of aphasia in Chinese. Study selection: After the raw screen on the data, pertinent literature about the mechanism on onset and recovery of aphasia were selected. Non-randomized clinical trials were excluded, and randomized controlled trials (RCT) were included through the screen on full test to determine whether a RCT or not. Either single and double-blinded or unblended RCT were eligible. Data extraction: Of the 34 articles on the onset and recovery mechanism of aphasia extracted, only 26 articles met the inclusion criteria. The eight articles excluded described the same trial. Data synthesis: Twenty-six trials were included for a total of 620 patients to discuss the mechanism of onset and recovery for aphasia respectively. Conclusion: There is no agreement about the mechanism of onset and recovery of aphasia. Hypoperfusion and hypometabolism to language center may be the pathogenesis of aphasia, and brain plasticity may be the recovery mechanism of aphasia.