Under extreme conditions such as flood season, leakage is the precursor of dam burst and dam break. The key measure to cut off the disaster chain of dam break is emergency handling of leakage timely and effectively. Based on a new method of emergency sealing leakage passage with underwater melting phase-change materials, the experimental studies of "self-inhaled" sealing of leakage passage and underwear melting of the paraffin wax are carried out, the sealing effects are analyzed and the relevant laws are summarized in this paper. Moreover, by measuring the paraffin wax in the leakage passage segmentally, the mass distribution curve of the sealing material along the sealing length is smoothed by convolution, the distribution of the solidified paraffin wax in the leakage passage is described qualitatively and the residual material after the sealing is analyzed. The analysis results show that the melted paraffin wax has good bonding with the surrounding water and is easy to gush into the leakage passage to achieve stable sealing in the process of sealing. Furthermore, the sealing length and the amount of effective sealing material are positively correlated with the initial leakage velocity, and the sealing intensity decreases with the increase of the initial leakage velocity. According to the characteristics of the paraffin wax sealing state, the sealing length can be divided into fractured compact section, loose fractured section and fractured compact section. After the sealing is completed, the residual material profile in the equipment is "wedge-shaped", and the fluctuation of residual mass is slight.