In order to solve the problem that Bulk Acoustic Wave (BAW) filter and the test instrument cannot be directly tested due to different interface forms, an on board test fixture for BAW filter is designed in this paper. Firstly, the thickness parameter of the dielectric substrate of the test fixture was preliminarily determined according to the experience formula,and the initiallength and width of the micro strip transmission line of the test fixture were calculated by the tool LineCaclin ADS. Secondly, the TDR transient simulation circuit was established in ADS to study the impedance mismatching of micro strip line, and the methods to solve the mismatching were presented. And then, the initial structural parameters of the designed fixture were imported into ADS for checking the impedance matching. Finally threeBAW filters with different center frequency were selected as the device under test (DUT) respectively to do the on wafer probe and the on board fixture test. Three comparisons of S12 on board vs S12 on wafer,S12 on board vs S21 on board,S11 on board vs S22 on board were carried out according to the test results of the scattering parameter matrix parameters(S11、S12、S21、S22) curves of the same filter. The comparison resultsshow that the whole test curve of on board fixture test is slightly offset fromthat on wafer probe test, but the trend of the whole curve is consistent, the S12 S21 and S11 S22 curves of the on board test areall in good agreement.The on board fixture test results can provide a reliable initial value for subsequent de embedding calibration.