A process for preparing an ultra-high-count filament yarn of polyimide - polysulfonamide electrospun fiber, comprising the steps of: step 1: after a monomer and a monomer are purified, adding the monomer and the monomer to a polymerization reactor together with a solvent to obtain a polyamic acid solution, then mechanically mixing with PSA to obtain a spinning raw material liquid of the polyamic acid and the PSA; step 2: implementing electrostatic spinning to the spinning raw material liquid in a high-voltage electric field, and collecting to obtain a polyamic acid/PSA electrospun fiber felt or nonwoven fabric using a stainless steel mesh belt as a collector; step 3: cutting the polyamic acid/PSA electrospun fiber felt or nonwoven fabric obtained above into slender strips with a width of 0.5 to 5.0 cm, and thermally drafting and imidizing the strips to form an oriented electrospun fiber bundle; step 4: twisting the above electrospun fiber bundle to obtain an ultra-high-count filament yarn of PI-PSA electrospun composite fibers, wherein, the monomer is a dianhydride which has the following structural formula: the monomer is a diamine which has the following structural formula: H 2 N-R 2 -NH 2; the obtained polyimide has the following chemical structure formula: wherein n and m values are natural numbers between 100 and 500; R 1 is the residue structure of C4-C30 dianhydride monomer, and is one or more selected from the group consisting of pyromelliticdianhydride group, biphenyl dianhydride residue, diphenylsulfonedianhydride residue, triphenylenedietherdianhydride residue, terephthalicdianhydride residue, 2.6-biphenyl pyrimidine dianhydride residue, benzophenonedianhydride residue, 3,6 bridged alkene cyclohexane tetracarboxylicdianhydride residue, hexafluoroacetonediphenyldianhydride residue, diphenoldiphenyldietherdianhydride residue, diphenyl sulfide dianhydride residue, diphenyl sulfide dianhydride residue, and2,2-acetone biphenyl dianhydride residue; R 2 is the residue structure of C6-C30 diamine monomer and is one or more selected from the group consistingof diphenyl ether diamine residue, p-phenylenediamine residue, dimethoxybenzidine residue, diphenylmethanediamine residue, m-phenylenediamine residue, biphenyldiamine residue, diphenoxydiphenoldiamine residue, 2-methyldiphenyl ether diamine residue, 2,6-pyrimidine diphenyldiamine residue, and (3,3'-dimethyl) diphenylmethanediamine residue; the ratio of two polymers PI and PSA, i.e, the mass ratio x/y =:. step 1: after a monomer and a monomer are purified, adding the monomer and the monomer to a polymerization reactor together with a solvent to obtain a polyamic acid solution, then mechanically mixing with PSA to obtain a spinning raw material liquid of the polyamic acid and the PSA; step 2: implementing electrostatic spinning to the spinning raw material liquid in a high-voltage electric field, and collecting to obtain a polyamic acid/PSA electrospun fiber felt or nonwoven fabric using a stainless steel mesh belt as a collector; step 3: cutting the polyamic acid/PSA electrospun fiber felt or nonwoven fabric obtained above into slender strips with a width of 0.5 to 5.0 cm, and thermally drafting and imidizing the strips to form an oriented electrospun fiber bundle; step 4: twisting the above electrospun fiber bundle to obtain an ultra-high-count filament yarn of PI-PSA electrospun composite fibers, wherein, the monomer is a dianhydride which has the following structural formula: the monomer is a diamine which has the following structural formula: H 2 N-R 2 -NH 2; the obtained polyimide has the following chemical structure formula: wherein n and m values are natural numbers between 100 and 500; R 1 is the residue structure of C4-C30 dianhydride monomer, and is one or more selected from the group consisting of pyromelliticdianhydride group, biphenyl dianhydride residue, diphenylsulfonedianhydride residue, triphenylenedietherdianhydride residue, terephthalicdianhydride residue, 2.6-biphenyl pyrimidine dianhydride residue, benzophenonedianhydride residue, 3,6 bridged alkene cyclohexane tetracarboxylicdianhydride residue, hexafluoroacetonediphenyldianhydride residue, diphenoldiphenyldietherdianhydride residue, diphenyl sulfide dianhydride residue, diphenyl sulfide dianhydride residue, and2,2-acetone biphenyl dianhydride residue; R 2 is the residue structure of C6-C30 diamine monomer and is one or more selected from the group consistingof diphenyl ether diamine residue, p-phenylenediamine residue, dimethoxybenzidine residue, diphenylmethanediamine residue, m-phenylenediamine residue, biphenyldiamine residue, diphenoxydiphenoldiamine residue, 2-methyldiphenyl ether diamine residue, 2,6-pyrimidine diphenyldiamine residue, and (3,3'-dimethyl) diphenylmethanediamine residue; the ratio of two polymers PI and PSA, i.e, the mass ratio x/y =:.