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Om diagnostic is useful in establishing the properties of DE at low redshifts. The constant Om indicates that the DE is the cosmological constant and the bigger value of Om shows that w is bigger [5]. Om ( z ) is less sensitive to observational errors than EOS w ( z ). Due to the degeneracy between Ω$_{m}$$_{0}$ and w , the property of w ( z ) depends on the current value of matter energy density Ω$_{m}$$_{0}$. However, Om diagnostic provides a null test of the cosmological constant without knowing the exact value of Ω$_{m}$$_{0}$. To reconstruct Om ( z ), we need to apply the specific model and model parameters. Following [11], we consider the uncertainties of Ω$_{m}$$_{0}$, w$_{0}$ and w$_{a}$ when we we reconstruct Om ( z ). 

