  In this paper, we study the cosmic constraint to $w$CDM model via $118$
strong gravitational lensing systems which are complied from SLACS, BELLS, LSD
and SL2S surveys, where the ratio between two angular diameter distances
$D^{obs} = D_A(z_l,z_s)/D_A(0,z_s)$ is taken as a cosmic observable. To obtain
this ratio, we adopt two strong lensing models: one is the singular isothermal
sphere model (SIS), the other one is the power-law density profile (PLP) model.
Via the Markov Chain Mote Carlo method, the posterior distribution of the
cosmological model parameters space is obtained. The results show that the
cosmological model parameters are not sensitive to the parameterized forms of
the power-law index $\gamma$. Furthermore, the PLP model gives a relative
tighter constraint to the cosmological parameters than that of the SIS model.
The predicted value of $\Omega_m=0.31^{+0.44}_{-0.24}$ by SIS model is
compatible with that obtained by {\it Planck}2015: $\Omega_{m}=0.313\pm0.013$.
However, the value of $\Omega_m=0.15^{+0.13}_{-0.11}$ based on the PLP model is
smaller and has $1.25\sigma$ tension with that obtained by {\it Planck}2015
result. This discrepancy maybe come from the systematic errors.
