Abstract: Active noise barrier utilized active control system to increase the low-frequency effect of the barrier. The effect of active noise barrier was influenced by the locations of the error sensors. The optimization of the locations of the error sensors in the active noise barrier system was investigated. Two conclusions were obtained through numerical simulations and experiments: (1) When the error sensors' positions were above the secondary sources in three arrangements, the excess insertion losses in the "dark area" were greatest, especially when the observational points were far away from the barrier; (2) There was an optimized distance between the error errors and the secondary sources for achieving the greatest excess insertion loss in the "dark area", when the positions were above the secondary sources.