Based on the self-developed stress self-feedback pressure relief device, a visual pressure relief test of the fluid filling lining was carried out to quantitatively study the support effect under the action of three spring stiffness coefficients, three loading areas and four particle sizes of fluid sand. The study found that the fluid filling lining support process can be divided into two stages: fluid compression section and fluid discharge section. In the fluid compression section, the initial load reduction rate was up to 78%. When the lining pressure exceeded the threshold value of the relief valve, it entered the fluid discharge section. The relief valve automatically released the surrounding rock energy by releasing the fluid and the load reduction rate was up to 47%. The research showed that the smaller the fluid particle size, spring coefficient and relative loading area, the better the supporting effect of fluid filling lining. The study found that the fluid discharge cavity area expanded in the shape of a prismatic. With the increase of the loading area and the pressure relief threshold, the depth of the cavity area is decreased. The expansion model of the cavity area was established and the equation of the pressure area of the cavity area was given. The energy dissipation principle of the pressure relief support technology of fluid filling lining was analysed and the energy dissipation equation was given.