Abstract: The sealed target preparation technology based on Al heat-expanding characteristic was proposed and performed firstly for iodine artificial transmutation experiment. The ¹²⁹I transmutation experiment in Xi’an Pulsed Reactor needed small target dimension and low leakage rate. After cooling enough time, the Al sealing-head was quickly placed into the top of the Al shell which was at room temperature. And the target was sealed automatically when the sealing-head had expanded at room temperature. The method is easy to practice and there is no high temperature welding process in target preparation, so the target core state shouldn’t be changed, and it costs little. At the same time, the target meterial could release little unwanted gas in heating analysis and tolerate 600 ℃. The experience calculation formula was obtained for the matching dimensions of self-expanding sealing parts on several experiments with 6061 Al. The leakage rates of four real transmutation targets are lower than 5×10^-9 Pa•m³/s in reverse pressure leakage detection and can meet the requirement of transmutation experiment.