  Ultralight axion (ULA) can be one of the potential candidates for dark
matter. The extremely low mass of the ULA can lead to a de Broglie wavelength
the size of galaxies which results in a suppression of the growth of structure
on small scales. In this work, we forecast the constraint on the ULA particle
mass $m_{\text{a}}$ and relative fraction to dark matter $f_{\text{a}} =
\Omega_{\text{a}}/\Omega_{\text{d}}$ for the forthcoming Stage IV space-based
optical survey equipment $\it{CSST}$ (China Space Station Telescope). We focus
on the $\it{CSST}$ cosmic shear and galaxy clustering photometric surveys, and
forecast the measurements of shear, galaxy, and galaxy-galaxy lensing power
spectra (i.e. 3$\times$2pt). The effects of neutrino, baryonic feedback, and
uncertainties of intrinsic alignment, shear calibration, galaxy bias, and
photometric redshift are also included in the analysis. After performing a
joint constraint on all the cosmological and systematical parameters based on
the simulated data from the theoretical prediction, we obtain a lower limit of
the ULA particle mass $\text{log}_{10}(m_{\text{a}}/\text{eV}) \geqslant -22.5$
and an upper limit of the ULA fraction $f_{\text{a}} \leqslant 0.83$ at 95\%
confidence level, and $\text{log}_{10}(m_{\text{a}}/\text{eV}) \geqslant -21.9$
with $f_{\text{a}} \leqslant 0.77$ when ignoring the baryonic feedback. We find
that the CSST photometric surveys can improve the constraint on the ULA mass by
about one order of magnitude, compared to the current constraints using the
same kind of observational data.
