Taiji, a space-based gravitational-wave observatory, consists of three satellites forming an equilateral triangle with arm length of $3\times {10}^6$ km, orbiting around the Sun. Taiji is able to observe the gravitational-wave standard siren events of massive black hole binary (MBHB) merger, which is helpful in probing the expansion of the universe. In this paper, we preliminarily forecast the capability of Taiji for improving cosmological parameter estimation with the gravitational-wave standard siren data. We simulate five-year standard siren data based on three fiducial cosmological models and three models of MBHB's formation and growth. It is found that the standard siren data from Taiji can effectively break the cosmological parameter degeneracies generated by the cosmic microwave background (CMB) anisotropies data, especially for dynamical dark energy models. The constraints on cosmological parameters are significantly improved by the data combination CMB + Taiji, compared to the CMB data alone. Compared to the current optical cosmological observations, Taiji can still provide help in improving the cosmological parameter estimation to some extent. In addition, we consider an ideal scenario to investigate the potential of Taiji on constraining cosmological parameters. We conclude that the standard sirens of MBHB from Taiji will become a powerful cosmological probe in the future.

天基引力波天文台太极由三颗卫星组成一个等边三角形，臂长为$\mathrm{3个}\times {10}^{\mathrm{6个}}$公里，绕太阳公转。太极能够观测到大质量黑洞双星（MBHB）并合的引力波标准海妖事件，有助于探测宇宙膨胀。在本文中，我们初步预测了太极利用引力波标准警报器数据改进宇宙学参数估计的能力。我们基于三个基准宇宙学模型和三个 MBHB 形成和增长模型模拟了五年标准海妖数据。发现来自太极的标准警报器数据可以有效打破宇宙微波背景（CMB）各向异性数据产生的宇宙学参数简并，特别是对于动态暗能量模型。CMB+太极数据组合显着改善了对宇宙学参数的约束，与单独的 CMB 数据相比。相较于目前的光学宇宙学观测，太极在一定程度上仍能为改进宇宙学参数估计提供帮助。此外，我们考虑了一个理想的场景来研究太极在约束宇宙学参数方面的潜力。我们得出结论，来自太极的 MBHB 标准警报器将成为未来强大的宇宙探测器。