Abstract: With the method of visible observation, experimental study on characteristics of stratification between hot and cold fluid was made in three different experimental tubes. In the meantime, according to the condition in which the force acted on the interface was balanced, analyses on the stability of fluid stratification in the density lock were done. The results show that in steady state conditions, there is an interface layer between hot and cold fluids in the density lock, and also there is a large temperature gradient in the interface layer. The stability of this layer is affected by velocity of disturbance on the interface and the temperature gradient in the interface layer. The stable interface layer plays an active role in preventing hot and cold fluids from being mixed. Besides, contrastive experiments on characteristics of fluid stratification were made when there was a partition or not respectively in experimental tubes. It shows that the honey comb channel in the density lock not only benefits for the stability of interface layer, but also is lucrative for the control on the position of interface.