The origin of the fractional state at ν = 1/2 observed in double-layer quantum Hall systems has been under debate for decades. Because of the variation of bilayer charge distribution and interlayer tunneling strength, the half-filling state can be attributed to a two-component(2C) or a onecomponent(1C) origin, which corresponds to Halperin state and Pffafian state, respectively. Here we report the magnetotransport measurement in decoupled twisted double bilayer graphene(TDBG), which has been proved to be a promising platform for double quantum Hall system. Fractional quantum hall states in both odd and even denominator fillings are observed. We also found that the half-filling state occurs at zero displacement field at νtot =-1/2, which is theoretically consistent with two-component Halperin-Laughlin (Ψ331) state. Moreover, we report the transition from two-component state at zero D field to one-component non-Abelian state by tunning displacement field. Our observation of the half filling state and its transition from 2C to 1C state provides the tunability of decoupled twisted double bilayer graphene and shed light on the understanding of the ground states at half-filling factor in the double quantum Hall system.