  We study the chiral phase transition with 2 + 1 quark flavors in an improved
soft-wall AdS/QCD model, which can produce the light meson spectrum and many
other low-energy quantities consistent with experiments in the two-flavor case.
The chiral transition behaviors of the quark condensates at different quark
masses are analysed in detail, and the (m_{u,d}, m_s) phase diagram for the
quark sector has been obtained from the improved soft-wall model. We find that
the features of the calculated phase diagram are completely consistent with the
standard scenario, which is supported by lattice simulations and theoretical
arguments. The evidence of a tricritical point on the m_{u,d} = 0 boundary of
the (m_{u,d}, m_s) phase diagram is first clearly presented in the bottom-up
AdS/QCD.
