−3 −2.5 −2 −1.5 −1 −0.5 0 −20 −15 −10 −5 0 5 w$_{0}$ w a SN SN+BaoR SN+Bao2 SN+BaoZ SN+Bao4 SN+Bao4+wmap (a) −5 −4.5 −4 −3.5 −3 −2.5 −2 −1.5 −1 −0.5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 w$_{0}$ a w a SN SN+BaoR SN+Bao2 SN+BaoZ SN+Bao4 SN+Bao4+wmap −20 −15 −10 −5 0 0 0.5 1 1.5 2 (b) −5 −4.5 −4 −3.5 −3 −2.5 −2 −1.5 −1 −0.5 0 0 0.5 1 1.5 2 2.5 w$_{0}$ a w a SN SN+BaoR SN+Bao2 SN+BaoZ SN+Bao4 SN+Bao4+wmap −20 −15 −10 −5 0 0 0.5 1 1.5 2 2.5 (c) −5 −4.5 −4 −3.5 −3 −2.5 −2 −1.5 −1 −0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 w$_{0}$ a w a SN SN+BaoR SN+Bao2 SN+BaoZ SN+Bao4 SN+Bao4+wmap −20 −15 −10 −5 0 0 1 2 3 4 5 (d) FIG. 2: The marginalized 1 σ contours of w$_{0}$ ( w a $_{0}$) and w$_{a}$ . The label of contours is the same as Fig. 1. (a) is for the CPL model with Sdss2 SNIa data. (b)-(d) are for the Wetterich model. The SNIa used in (b)-(d) are Csta, Cstd and Sdss2, respectively. Fig. 1 shows contours of the fitting results for the CPL parametrization by combining different SNIa data together with different BAO data and the combination of the WMAP5 data. The SNIa data used in Figs. 1a-1d and 2a are Csta, Cstb, Cstc, Cstd, and Sdss2, respectively. The green lines are for using just SNIa data alone with different templates. The dashed black lines are for SN+BaoR, the cyan lines are for SN+Bao2. Since the BaoR data is derived from Bao2 data, so the result using BaoR data is compatible with that of Bao2. Also we can see that the constraint is a little better with Bao2 than that with BaoR. The magenta lines are for SN+BaoZ, we see that the constraint from BaoZ is in general consistent with that from Bao2 although the former gives a little tighter constraint. These behaviors keep 8