To improve the tuning relation accuracy of an acousto-optic tunable filter, the conventional separated laser and broadband light methods were combined. The single laser test measured one accurate point and corrected the large amounts of data obtained from the broadband light method. The final tuning relation was fitted by the corrected data. A simulation and an experiment for several methods were conducted for comparison. The relative error was reduced from 0.2% to 0.05% in the 430 - 785??nm range. The equivalent wavelength accuracy improved from 1 to 0.2 nm. This method solved the problems associated with the use of a single laser source with few test data values and a single broadband light source with poor collimation.