We analyze the dephasing and disorder effects in 2D quantum spin Hall insulators (QSHI) and 3D topological insulators.For the QSHI, we find that the quantum resistance plateaus are robust against the normal dephasing but fragile with the spin dephasing.For 3D topological insulators, we show that the combination of dephasing and impurity scattering can cause backscattering in the helical states.Especially for the charge impurity case, the backscattering cross-section becomes extremely large around the Dirac point, which can lead to the anomalous gap-like features found in recent experiments [Nat.Phys.{f7}, 840 (2011)].Moreover, we study the disorder effects in Bernevig-Hughes-Zhang (BHZ) model (unitary system), and find that the Anderson transition of QSHI is determined by the model parameters.In contrast to the common belief that 2D unitary system scales to insulator except at certain critical points, we find that an exotic metallic phase emerges between QSHI and normal insulator phases in InAs/GaSb-type BHZ model.