A process for preparing a poly(meth)acrylimide foam by a one-step feeding gelation, comprising the following steps: uniformly mixing a functional monomer, a solubility adjusting monomer, a dispersing aid, an initiator, a crosslinking agent, a nucleating agent, a foaming agent and a functional filler, followed by adding a gelation promoter, dispersing uniformly, and then injecting into a closed planar mold and performing polymerization in a 38-50°C water bath; reducing the polymerization temperature by 2-10°C when the reaction is performed to form a uniform gel, and then continuously removing the reaction heat to maintain the temperature; gradiently increasing the temperature to 100-120°C after the gel is completely converted into a solid, to obtain a poly(methyl)acrylimide prepolymerized plate; foaming the poly(meth)acrylimide prepolymerized plat by heating at 140-230°C, to obtain the poly(meth)acrylimide foam, wherein the functional monomer is carboxyl group-containing acrylic monomers and nitrile group-containing monomers, wherein the solubility adjusting monomer is at least one of amide acrylic monomers, ester acrylic monomers, styrene and derivatives thereof, wherein the gelation promoter is (a) fumed nano titanium dioxide, (b) light magnesium oxide, (c) light zinc oxide, (d) a mixture of hydrophilic fumed nano silica and light magnesium oxide in any ratio or (e) a mixture of fumed nano titanium dioxide and light magnesium oxide in any ratio, wherein the fumed nano titanium dioxide of the rutile and anatase type has a particle size of less than 100 nm; the light magnesium oxide has a specific surface area ≥50 m 2 /g; the light zinc oxide has a specific surface area of ≥45 m 2 /g; the hydrophilic fumed nano silica has a specific surface area of 100-400 m 2 /g. uniformly mixing a functional monomer, a solubility adjusting monomer, a dispersing aid, an initiator, a crosslinking agent, a nucleating agent, a foaming agent and a functional filler, followed by adding a gelation promoter, dispersing uniformly, and then injecting into a closed planar mold and performing polymerization in a 38-50°C water bath; reducing the polymerization temperature by 2-10°C when the reaction is performed to form a uniform gel, and then continuously removing the reaction heat to maintain the temperature; gradiently increasing the temperature to 100-120°C after the gel is completely converted into a solid, to obtain a poly(methyl)acrylimide prepolymerized plate; foaming the poly(meth)acrylimide prepolymerized plat by heating at 140-230°C, to obtain the poly(meth)acrylimide foam, wherein the functional monomer is carboxyl group-containing acrylic monomers and nitrile group-containing monomers, wherein the solubility adjusting monomer is at least one of amide acrylic monomers, ester acrylic monomers, styrene and derivatives thereof, wherein the gelation promoter is (a) fumed nano titanium dioxide, (b) light magnesium oxide, (c) light zinc oxide, (d) a mixture of hydrophilic fumed nano silica and light magnesium oxide in any ratio or (e) a mixture of fumed nano titanium dioxide and light magnesium oxide in any ratio, wherein the fumed nano titanium dioxide of the rutile and anatase type has a particle size of less than 100 nm; the light magnesium oxide has a specific surface area ≥50 m 2 /g; the light zinc oxide has a specific surface area of ≥45 m 2 /g; the hydrophilic fumed nano silica has a specific surface area of 100-400 m 2 /g.