Objective: To evaluate the relationship between the status of collateral circulation provided by multiphase CT angiography and the benefit and risk of vascular recanalization in patients with middle cerebral artery (MCA) occlusion. Methods: This retrospective study included 49 patients diagnosed with acute MCA occlusion and treated with rt-PA in the First Affiliated Hospital of Nanjing Medical University from October 2017 to September 2018. According to the ASPECTS collateral circulation score, the patients were divided into two groups: good collateral group (n=31) and poor collateral group (n=18). The benefits and risks after thrombolysis in the two groups were compared, including 24-h NIHSS score, 30-day mortality, 90-day modified rankin scale (mRS) score, and the incidence of symptomatic cerebral hemorrhage. Statistical analysis was performed using t test, corrected χ² test, or Fisher's exact test. Results: The 24-h NIHSS score and 90-day mRS score in the good collateral group were significantly lower than those in the poor collateral group (4.6±5.6 vs 12.5±8.4, P=0.00; 1.7±1.7 vs 3.1±1.5, P<0.05). The incidence of NIHSS score improved by ≥50% and the incidence of 90-day mRS 0-2 was significantly higher in the good collateral group after 24 h of thrombolysis (77.4% vs 27.8%, P<0.05; 80.6% vs 27.8%, P=0.00); The incidence of symptomatic cerebral hemorrhage was significantly lower in the good collateral group than in the poor group (9.7% vs 50.0%, P<0.05). There was no significant difference in mortality between the two groups after 30 days of thrombolysis (P>0.05), but the 30-day mortality of the poor collateral group was still greater than that of the good collateral group (11.1% vs 0%). Conclusion For patients with acute MCA infarction and receiving vascular recanalization therapy, patients with good collateral circulation can achieve good clinical outcomes, restore better recent neurological function, and obtain lower incidence of symptomatic cerebral hemorrhage and lower disability and mortality rate.