  Chiral phase transition for three-flavor $N_f=2+1$ QCD with $m_u=m_d\neq m_s$
is investigated in a modified soft-wall holographic QCD model. Solving
temperature dependent chiral condensates from equations of motion of the
modified soft-wall model, we extract the quark mass dependence of the order of
chiral phase transition in the case of $N_f=2+1$, and the result is in
agreement with the "Colombia Plot", which is summarized from lattice
simulations and other non-perturbative methods. First order phase transition is
observed around the three flavor chiral limit $m_{u/d}=0, m_{s}=0$, while at
sufficient large quark masses it turns to be a crossover phase transition. The
first order and crossover regions are separated by a second order phase
transition line. The second order line is divided into two parts by the
$m_{u/d}=m_s$ line, and the $m_s$ dependence of the transition temperature in
these two parts are totally contrast, which might indicate that the two parts
are governed by different universality classes.
