In this paper,we use symbolic transfer entropy to study the coupling strength between premature signals.Numerical experiments show that three types of signal couplings are in the same direction.Among them,normal signal coupling is the strongest,followed by that of premature ventricular contractions,and that of atrial premature beats is the weakest.The T test shows that the entropies of the three signals are distinct.Symbolic transfer entropy requires less data,can distinguish the three types of signals and has very good computational efficiency. In this paper, we use symbolic transfer entropy to study the coupling strength between premature signals. Numerical experiments show that three types of signal couplings are in the same direction. Among them, normal signal coupling is the strongest, followed by that of premature ventricular contractions , and that of atrial premature beats is the weakest.The T test shows that the entropies of the three signals are distinct.Symbolic transfer entropy requires less data, can distinguish the three types of signals and has very good computational efficiency.