The test site setup from 30 MHz to 200 MHz of Absorber Lined Shielded Enclosure (ALSE) performance validation of the CISPR 25 [1] is improved and optimized in this paper. By effectively grounding to the test bench, the scattering resonance in radiation emission measurement of vehicle parts is resolved. The setup of the test site is modeled by full-wave simulation software. Additionally, with the back edge of the test bench is grounded, both the front edge and the two side edges and are grounded separately. The simulation results and exploring test show that grounding at the front edge of the test bench can better suppress the scattering resonance and reduce the defined tolerance of the CISPR 25 to 5 dB creatively. The new test site setup improves the reliability, the accuracy and the consistency in the radiation emission measurement.