The invention discloses an experiment device for synthesizing a marine 
natural gas hydrate sample. The device comprises a reaction kettle, an 
axial compression piston, a kettle outer jacket, an injection 
system, an 
axial compression control system, a confining 
pressure control system and an output 
system. The invention further discloses an experiment method adopting the experiment device for synthesizing the marine 
natural gas hydrate sample. The method comprises the steps that firstly, ice 
powder particles are manufactured, then, the ice 
powder particles and dried 
porous medium particles are mixed and placed into the high-pressure reaction kettle in the subzero low-temperature environment so as to simulate 
seabed geomechanical properties, then, 
methane is injected to generate a 
hydrate, ice is directly converted into the hydrate, and finally 
free gas inside the reaction kettle is removed through the 
liquid injection system. According to the experiment device and method, true marine 
natural gas hydrate samples which are hard to obtain on various geological conditions and various occurrence form conditions can be economically, efficiently and accurately obtained, the research on the hydrate is closer to the reality, and the experiment basis is provided for research of natural gas hydrate exploitation.