Currently, diagnosis of insomnia is mainly assessed through standardized scales, lacking an objective basis for assessment. Patients with insomnia usually exhibit symptoms such as memory loss and poor concentration. The prefrontal lobe of the brain plays a vital role in performing cognitive tasks, and chronic insomnia can cause structural changes to the prefrontal lobe of the brain that can affect cognitive performance. The verbal fluency task (VFT) is a commonly used cognitive testing task in the field of neuroscience. In this paper, we combined acupuncture with the treatment of insomnia patients and applied functional near-infrared spectroscopy (fNIRS) equipment to collect prefrontal brain oxygen signals in the VFT in insomnia patients before acupuncture versus after four weeks of acupuncture. In assessing cognitive performance, the integral value of oxygenated hemoglobin (HbO2) concentration in prefrontal channels was extracted to indicate the degree of activation, and the activation of different prefrontal channels was observed. It was found that the integral value of the mean prefrontal channel in the group of insomniacs before acupuncture was 0.49, the integral value of the mean channel in the group of insomniacs after four weeks of acupuncture treatment increased to 1.41, and the amount of change in the mean value of the HbO2 concentration was enhanced in channels 1 and 19. This study confirms that acupuncture treatment can enhance the degree of activation and the amount of change in prefrontal cerebral oxygen signaling in patients with insomnia, which can help to improve the cognitive performance of patients with insomnia and make fNIRS an objective assessment tool for diagnosing insomnia.