  We investigate the quark number fluctuations up to the fourth order in the
matter composed of two light flavor quarks with isospin symmetry and at finite
temperature and finite chemical potential using the Dyson-Schwinger equation
approach of QCD. In order to solve the quark gap equation, we approximate the
dressed quark-gluon vertex with the bare one and adopt both the Marris-Tandy
(MT) model and the infrared constant (Qin-Chang) model for the dressed gluon
propagator. Our results indicate that the second, third, and forth order
fluctuations of net quark number all diverge at the critical end point (CEP).
Around the CEP, the second order fluctuation possesses obvious pump while the
third and fourth order ones exhibit distinct wiggles between positive and
negative. For the MT model and the Qin-Chang model, we give the pseudo-critical
temperature at zero quark chemical potential as $T_{c}=146$ MeV and $150$ MeV,
and locate the CEP at $({\mu_{E}^{q}}, {T_{E}^{}}) = (120, 124)$ MeV and
$(124,129)$ MeV, respectively. In addition, our results manifest that the
fluctuations are insensitive to the details of the model, but the location of
the CEP shifts to low chemical potential and high temperature as the
confinement length scale increases.
