  Hundreds of 650 MHz superconducting radio-frequency (SRF) cavities with high
intrinsic quality factor (Q0) and accelerating gradient (Eacc) will be adopted
for Circular Electron Positron Collider (CEPC). The values of Q0 and Eacc are
obtained during vertical test at 2.0 K. Hence, high accuracy of vertical test
is essential for evaluating the performance of SRF cavity. The 650 MHz SRF
cavities achieved very high Q0 (6E10) and Eacc (40 MV/m) during the vertical
test. In our study, the error analysis of vertical test was conducted in the
scalar case, in order to achieve high accuracy. The uncertainties of vertical
test were obtained through calculation, which was approximately 3% for Eacc and
less than 5% for Q0. This result was reasonable and acceptable.
