  Space-based gravitational wave detection is extremely sensitive to
disturbances. The Keplerian configuration cannot accurately reflect the
variations in spacecraft configuration. Planetary gravitational disturbances
are one of the main sources. Numerical simulation is an effective method to
investigate the impact of perturbation on spacecraft orbits. This study shows
that, in the context of the Taiji project, Earth's gravity is an essential
factor in the change in heliocentric formation configuration, contributing to
the relative acceleration between spacecrafts in the order of $\mathcal
O(10^{-6})\,{\rm m\cdot s^{-2}}$. Considering 00:00:00 on 27 October 2032 as
the initial orbiting moment, under the influence of Earth's gravitational
perturbation, the maximum relative change in armlengths and variation rates of
armlengths for Taiji is $1.6\times 10^{5}\,{\rm km}$, $32\,{\rm m\cdot
s^{-1}}$, respectively, compared with the unperturbed Keplerian orbit.
Additionally, by considering the gravitational perturbations of Venus and
Jupiter, the armlength and relative velocity for Taiji are reduced by $16.01\%$
and $17.45\%$, respectively, compared with when only considering that of Earth.
The maximum amplitude of the formation motion indicator changes with the orbit
entry time. Results show that the relative velocity increase between the
spacecrafts is minimal when the initial orbital moment occurs in July.
Moreover, the numerical simulation results are inconsistent when using
different ephemerides. The differences between ephemerides DE440 and DE430 are
smaller than those between DE440 and DE421.
