Abstract: In the present study, the evolution of double-diffusive convection is explored in a linear stratified salt-water system, where the uniform heating is provided from below and the constant temperature is applied from above. By using the variances of vertical profiles of temperature and shadowgraph images, it is found that the generating and merging of the staircases occur during the experiment. Based on the temperature difference across the system, the whole evolution process can be divided into two stages. In the temperature difference increase stage, the generation of new staircase happens at the top of the old ones, while the merging event typically occurs between the lowest staircase and its overlaying one. The staircase number increases because that the generating rate of new staircase is faster than the merging rate. In the temperature difference decrease stage, the existing staircases disappear progressively. It is interesting that the bottom boundary of system can feel the happen of the merging events of the lowest staircase, which means that the dynamics process in the local region can have effect on the other regions of system. The thickness of the lowest staircase (h) is much thicker than those of others, and its temporal dependence is in the form of h~τ^0.7, here τ is the dimensionless time.