The invention provides a heat accumulator with a safety valve with super large displacement and a conventional safety valve and a heat accumulating method. The mode that a heat accumulator is directly connected with a test safety valve through bolts is adopted in all existing safety valve test systems. Steam is vented into the heat accumulator from a boiler, the pressure in the heat accumulator is made to rise gradually, after the pressure reaches the opening pressure of the test safety valve, the test safety valve is opened. The heat accumulator with the safety valve with the super large displacement and the conventional safety valve comprises a test safety valve pipe seat (5) which is connected with a flange (4), the flange is connected with a shell (6), the shell is connected with a support (11) and a manhole seat (7), the manhole seat is connected with a manhole (8), a steam and water separator (1), a steam distributing device (2) and a perforated pipe diffuser (3) are installed inside the shell, and a set of diffusion holes are machined in the perforated pipe diffuser. The heat accumulator with the safety valve with the super large displacement and the conventional safety valve and the heat accumulating method are applied to a heat accumulator of the boiler.