Objective: To investigate the brain function and their correlation with sleep beliefs and attitudes in adolescents with drug naive insomnia by using fractional amplitude of low frequency fluctuation, so as to provide a reference for the mechanism and treatment of insomnia. Methods: An insomnia group ( n =21) recruited first episode, drug naive, adolescents with insomnia who met the diagnostic criteria of the American Diagnostic and Statistical Manual of Mental Disorders(DSM-V). Healthy subjects matched with age, gender, and educational background were selected as the control group ( n =20). Pittsburgh Sleep Quality Index Scale (PSQI), Brief Version of Dysfunctional Beliefs and Attitudes about Sleep (DBAS-16), 24 Items Hamilton Depression Scale (HAMD-24), 14 Items Hamilton Anxiety Scale (HAMA-14) were evaluated. Fractional amplitude of low frequency fluctuation was used for analysis, and Pearson correlation analysis was employed to quantify the correlation between peak values of brain regions with significant differences and the clinical scale scores of the two groups. Results: Compared with the control group, ractional amplitude of low frequency fluctuation(fALFF) values in the insomnia group were significantly decreased ( P <0.01, Alphaism corrected) in the left dorsolateral prefrontal lobe (L-DLPFC, MNI coordinates: -12, 60, 21, t =-3.85, K =495) and the left precuneus (MNI coordinates: -3, -54, 51, t =-4.29, K =417). The fALFF value of L-DLPFC in the insomnia group was positively correlated with DBAS-16 score ( r= 0.47 , P = 0.04 ). Conclusion Abnormalities in the L-DLPFC region suggest that adolescents with insomnia may suffer from impaired regulation of emotional and cognitive activities related to sleep.