  The detection of stochastic gravitational wave background (SGWB) is among the
leading scientific goals of the space-borne gravitational wave observatory,
which would have significant impact on astrophysics and fundamental physics. In
this work, we developed a data analysis software, \texttt{TQSGWB}, which can
extract isotropic SGWB using the Bayes analysis method based on the TianQin
detector. We find that for the noise cross spectrum, there are imaginary
components and they play an important role in breaking the degeneracy of the
position noise in the common laser link. When the imaginary corrections are
considered, the credible regions of the position noise parameters are reduced
by two orders of magnitude. We demonstrate that the parameters of various
signals and instrumental noise could be estimated directly in the absence of a
Galactic confusion foreground through Markov chain Monte Carlo sampling. With
only a three-month observation, we find that TianQin could be able to
confidently detect SGWBs with energy density as low as $\Omega_{\rm PL} = 1.3
\times 10^{-12}$, $\Omega_{\rm Flat} = 6.0 \times 10^{-12}$, and $\Omega_{\rm
SP} = 9.0 \times 10^{-12}$, for power-law, flat, and single-peak models
respectively.
