A high-grafting density cyclic comb shaped polymer and a preparation method therefor. The method comprises the following steps : 1) synthesizing linear poly(pentafluorophenyl 4-vinylbenzoate) (l-PPF4VB4.0k); 2) performing photo-induced cyclization on the linear polymer to prepare a cyclic polymer (c-PPF4VB4.0k); 3) performing post modification on the cyclic polymer c-PPF4VB4.0k by using small molecules to prepare a functionalized cyclic polymer (c-P1); 4) then performing polymer post modification on the cyclic polymer (c-P1) by using an efficient click reaction to construct a high-grafting density cyclic comb shaped polymer (c-P1-g-PS); and 5) directly performing polymer post modification on the cyclic polymer c-PPF4VB4.0k by using macromolecules to construct a high-grafting density cyclic comb shaped polymer (c-PPF4VB4.0k-g-PEG), the obtained cyclic comb shaped polymer still remaining the characteristic of a narrow molecular weight distribution.