Abstract: Based on 1/3 rate Turbo codes whose memory order is m , three trellis termination schemes are studied: the conventional trellis termination scheme, which only makes one sub encoder have all zero state at the end of encoding; the trellis termination scheme proposed in this paper, which makes two sub encoders have all zero state at the end of encoding and makes the first m tail bits be interleaved and encoded; the trellis termination scheme recommended by 3GPP, which makes two sub encoders have all zero state at the end of encoding and doesn't make any tail bits be interleaved and encoded. Soft output Viterbi algorithm (SOVA) is applied to decoding Turbo codes. On the basis of the decoding principle, the scheme design, decoding performance and encoding efficiency of the three trellis termination schemes are analyzed and compared. The computer simulation results show that the proposed trellis termination scheme has the optimum "error floor" performance.