An eight-arm functional polyethylene glycol, wherein, the eight-arm functional polyethylene glycol has eight PEG chains and one octavalent central group CORE 8 as represented by wherein the moiety is denoted as "CORE" and consists of one tetravalent central group U and four trivalent branching groups E 1, E 2, E 3 and E 4; wherein, E 1, E 2, E 3 and E 4 are each independently identical or not identical in one molecule; wherein, L 11, L 12, L 21, L 22, L 31, L 32, L 41 and L 42 are divalent linking groups that respectively attaches a PEG chain to one of the eight ends of CORE; L 11, L 12, L 21, L 22, L 31, L 32, L 41 and L 42 are each independently present or absent, and can be each independently identical or not identical in one molecule; wherein, each PEG chain bears at least one terminal functional group F as represented by wherein, q and q 1 are each independently equal to 0 or 1; Z 1 and Z 2 are each independently a divalent linking group; R 01 is a functional end-group capable of generating a covalent bond, a dynamic covalent bond, dihydrogen-bonding, multiple hydrogen-bonding, therapeutic targeting binding or fluorescent response; wherein, the combination of D Emax, d DE and d E2 satisfies at least one of the following formulas: D Emax ≤100, d DE ≤21 and d E2 ≤10; wherein, D Emax represents "maximum chain length", and refers to the largest number of skeleton atoms between any two trivalent branching centers of the four trivalent branching groups E i (i = 1, 2, 3 and 4), wherein, the skeleton atoms between two trivalent branching centers cross U, but exclude the two branching points; wherein, D Emin refers to the minimum chain length between any two trivalent branching centers of E i (i = 1, 2, 3 and 4); wherein, d DE refers to the difference between D Emax and D Emin; wherein, d E2 refers to the length difference between the two branches which respectively starts from one branching center of E i (i = 1, 2, 3 or 4) to two oxygen atoms of the two corresponding PEG chains. wherein, L 11, L 12, L 21, L 22, L 31, L 32, L 41 and L 42 are divalent linking groups that respectively attaches a PEG chain to one of the eight ends of CORE; L 11, L 12, L 21, L 22, L 31, L 32, L 41 and L 42 are each independently present or absent, and can be each independently identical or not identical in one molecule; wherein, each PEG chain bears at least one terminal functional group F as represented by wherein, q and q 1 are each independently equal to 0 or 1; Z 1 and Z 2 are each independently a divalent linking group; R 01 is a functional end-group capable of generating a covalent bond, a dynamic covalent bond, dihydrogen-bonding, multiple hydrogen-bonding, therapeutic targeting binding or fluorescent response; wherein, the combination of D Emax, d DE and d E2 satisfies at least one of the following formulas: D Emax ≤100, d DE ≤21 and d E2 ≤10; wherein, D Emax represents "maximum chain length", and refers to the largest number of skeleton atoms between any two trivalent branching centers of the four trivalent branching groups E i (i = 1, 2, 3 and 4), wherein, the skeleton atoms between two trivalent branching centers cross U, but exclude the two branching points; wherein, D Emin refers to the minimum chain length between any two trivalent branching centers of E i (i = 1, 2, 3 and 4); wherein, d DE refers to the difference between D Emax and D Emin; wherein, d E2 refers to the length difference between the two branches which respectively starts from one branching center of E i (i = 1, 2, 3 or 4) to two oxygen atoms of the two corresponding PEG chains.