In this work , we explore the evolution of the dark energy equation of state \omega by using Chevalliear-Polarski-Linder ( CPL ) parametrization and the binned parametrizations . For binned parametrizations , we adopt three methods to choose the redshift interval : I . Ensure that ‘ ‘ \triangle z = const ’ ’ , where \triangle z is the width of each bin ; II . Ensure that ‘ ‘ n \triangle z = const ’ ’ , where n is the number of SNIa in each bin ; III . Treat redshift discontinuity points as models parameters , i.e . ‘ ‘ free \triangle z ’ ’ . For observational data , we adopt JLA type Ia supernova ( SNIa ) samples , SDSS DR12 data , and Planck 2015 distance priors . In particular , for JLA SNIa samples , we consider three statistic techniques : I . Magnitude statistics , which is the traditional method ; II . Flux statistics , which reduces the systematic uncertainties of SNIa ; III . Improve flux statistics , which can reduce the systematic uncertainties and give tighter constrains at the same time . The results are as follows : ( 1 ) For all the cases , \omega = -1 is always satisfied at 1 \sigma confidence regions ; It means that \Lambda CDM is still favored by current observations . ( 2 ) For magnitude statistics , ‘ ‘ free \triangle z ’ ’ model will give the smallest error bars ; this conclusion does not hold true for flux statistics and improved flux statistic . ( 3 ) The improved flux statistic yields a largest present fractional density of matter \Omega _ { m } ; in addition , this technique will give a largest current deceleration parameter q _ { 0 } , which reveals a universe with a slowest cosmic acceleration .