Inclusion Criteria1. Acute anterior circulation cerebral infarction diagnosed ≤ 48h;
2. First time diagnosed or have history of acute anterior circulation cerebral infarction without serious sequelae(mRS=0-2);
3. Age from 18 to 80 years old;
4. National Institute of Health stroke scale(NIHSS) from 6 to 25;
5. Have provided signed written informed consent from the patient or the patient's legal representative.
Exclusion Criteria1. Brain CT shows cerebral hemorrhage disease: cerebral hemorrhage, subarachnoid hemorrhage, etc.
2. Transient ischemic attack(TIA);
3. Serious disturbance of consciousness: Glasgow Coma ScaleGCS（GCS）≤8;
4. Combined angiotensin-converting enzyme inhibitor(ACEI) less than 5 half-time(according to its instruction), or need to be treated with ACEI;
5. Cases treated with thrombolysis / stent surgery or expected to be treated with thrombolysis / interventional therapy / stent surgery.
6. subjects with bleeding disorders at Past or present, laboratory tests: INR > 1.5 or APTT > 2 times;
7. subjects with abnormal liver function (ALT/AST > 1.5 * ULN) and abnormal renal function (Cr> normal upper limit);
8. subjects with history of epilepsy or other serious systemic disease before onset of AIS refused by PI to enroll ;
9. subjects with cardiogenic stroke or cardiogenic stroke related high-risk factors identified by PI, such as atrial fibrillation, echocardiography or Mural thrombus etc;
10. subjects diagnosised any malignancy (except basal cell carcinoma) within 5 years prior to the start of the study;
11. subjects with severe dementia or can't cooperate to evaluate identified by PI;
12. suffering from severe hypertension and failed to control :systolic blood pressure ≥200mmHg (26.6kPa) or diastolic blood pressure ≥110mmHg (14.6kPa); hypotension: systolic blood pressure＜ 90mmHg and/or diastolic blood pressure＜ 60mmHg
13. subjects be allergic or intolerant to kallikrein at past;
14. subjects be pregnant/lactating or possibly and planned pregnant;
15. subjects be unsuitable for this clinical study identified by PI.