  TianQin is a proposed space-based gravitational wave observatory. It is
designed to detect the gravitational wave signals in the frequency range of 0.1
mHz -- 1 Hz. At a geocentric distance of $10^5$ km, the plasma in the earth
magnetosphere will contribute as the main source of environmental noises. Here,
we analyze the acceleration noises that are caused by the magnetic field of
space plasma for the test mass of TianQin. The real solar wind data observed by
the Advanced Composition Explorer are taken as the input of the
magnetohydrodynamic simulation. The Space Weather Modeling Framework is used to
simulate the global magnetosphere of the earth, from which we obtain the plasma
and magnetic field parameters on the detector's orbits. We calculate the time
series of the residual accelerations and the corresponding amplitude spectral
densities on these orbit configurations. We find that the residual acceleration
produced by the interaction between the TM's magnetic moment induced by the
space magnetic field and the spacecraft magnetic field ($\bm{a}_{\rm M1}$) is
the dominant term, which can approach $10^{-15}$ m/s$^2$/Hz$^{1/2}$ at $f
\approx$ 0.2 mHz for the nominal values of the magnetic susceptibility
($\chi_{\rm m} = 10^{-5}$) and the magnetic shielding factor ($\xi_{\rm m} =
10$) of the test mass. The ratios between the amplitude spectral density of the
acceleration noise caused by the space magnetic field and the preliminary goal
of the inertial sensor are 0.38 and 0.08 at 1 mHz and 10 mHz, respectively. We
discuss the further reduction of this acceleration noise by decreasing
$\chi_{\rm m}$ and/or increasing $\xi_{\rm m}$ in the future instrumentation
development for TianQin.
