no improvement of χ 2 total,min compared to the case of 3 bins, which indicates there is no more turning points of w$_{de}$ in this region. As data points with z > 1 are rather less than those with z < 1, to see clearly the evolution behavior of EoS in the region of low redshift, we now focus on the region with z ∈ (0 , 0 . 9), avoiding the possible turning point around z = 1, and set the divided points as: (0 , z$_{1}$, 0 . 9 , ∞ ), i.e., We see from the top left panel of Fig. 2 that there are deviations of w$_{de}$ from − 1 around z = 0 and z = 0 . 45 beyond 1 σ , and around z = 0 . 9 the deviation is beyond 2 σ . We decorrelate the parameters in w$_{de}$ ( z ) by using the technique introduced in section II. The uncorrelated errors are shown in the bottom left panel of Fig. 2. In that case, there are no w$_{de}$ ( z ) =     w (0) + w ( z$_{1}$ ) − w (0) z$_{1}$ z , 0 < z ≤ z$_{1}$ w ( z$_{1}$ ) + w (0 . 9) − w ( z$_{1}$ ) 0 . 9 − z$_{1}$ ( z − z$_{1}$ ) , z$_{1}$ < z ≤ 0 . 9 − 1 , 0 . 9 < z < ∞ (27) z$_{1}$ = 0 . 45, and the best-fitted w$_{de}$ ( z ) is In this case, we obtain the best-fitted tuning point z$_{1}$ = 0 . 45, and the best-fitted w$_{de}$ ( z ) is shown in Fig. 1 (the red, dashed line) which almost coincides with the best-fitted w$_{de}$ ( z ) of Model I in z ∈ (0 , 0 . 9). This indicates that the data favor w$_{de}$ ( z ) to turn its evolution direction around z = 0 . 45, and favor an EoS with crossing the cosmological constant ( w = − 1) [29]. Then we obtain 1 σ and 2 σ errors of parameters by using the MCMC method. Here we have fixed z$_{1}$ = 0 . 45 in the process to obtain the errors of the parameters. Note that the errors of the parameters w$_{de}$ ( z$_{i}$ ) also represent errors of whole w$_{de}$ ( z ) in each bin, the 1 σ and 2 σ errors of w$_{de}$ ( z ) shown in Fig. 2 are obtained by connecting the corresponding error ranges of w$_{de}$ ( z$_{i}$ ). If another parameter set of w$_{de}$ ( z ) (as introduced in section II) was used, one will get the same result as that of Fig. 2. B. Model II TABLE II: The best-fitted parameters for Model I. parameters h Ω (0) b Ω (0) m z$_{1}$ z$_{2}$ w (0) w ( z$_{1}$ ) w ( z$_{2}$ ) w (1 . 8) w$_{L}$ best-fitted values 0.688 0.049 0.279 0.44 1.07 -0.63 -1.57 2.28 -16.84 { -1 } 10