Abstract: A boss structure sealing experiment device for an IV type hydrogen storage cylinder. The device includes a high-pressure chamber, a sealing leakage structure, a cylinder mouth valve, and a low-pressure chamber, where the high-pressure chamber, the sealing leakage structure, and the low-pressure chamber are tightly connected to one another through flange bolts, and the cylinder mouth valve is tightly connected to the high-pressure chamber through threads. Further disclosed is a sealing experiment system. The system includes a boss structure sealing experiment device, a high-pressure gas supply device, and a leaked gas detection device. The high-pressure gas supply device consists of a hydrogen source, a compressor, a buffer tank, a valve, and a pressure gauge; and the leaked gas detection device consists of a gas mixing chamber, a carrier gas, and a gas leakage detector. Further disclosed is a test method for a boss structure sealing experiment.