The effects of external optical feedback (OFB)on the oscillating characteristics of 980nm vertical-cavity surface-emitting lasers (VCSEL) were investigated. The OFB sensibility of VCSEL and edge emitting lasers (EEL) were evaluated by calculating OFB parameters. Based on the compound cavity theory, the effects of external optical feedback on the oscillating characteristic parameters of VCSEL, such as the threshold current and the differential quantum efficiency, were analyzed. The experimental results indicate that the threshold current of the VCSEL decreases from 0.63A to 0.59A when the feedback ratio is 10%. Meantime, the slope efficiency and the output power also decrease. The result of experiment is in goad agreement with the calculation.