The invention discloses a 7-ethyl-10-hydroxycamptothecine (SN38) conjugated polymer, a preparation method, a nano-preparation of the conjugated polymer and an anti-tumor application. C-10 position or C-20 position hydroxy of a 7-ethyl-10-hydroxycamptothecine compound is conjugated with different molecular weight terminal carboxyl group polymers through covalent bonds to obtain an SN38 series conjugated prodrug, and then amphiphilic polymer materials and the SN38 prodrug are prepared into a nano-drug. The nano-drug solves the problem of poor water solubility of SN38, and slow release of the SN38 is achieved in vitro. Besides, the particle diameter of the nano-drug is mainly distributed within the range of 20-50nm, high permeability and EPR (enhanced permeation and retention) effects of nano-particles through solid tumors are achieved, and passive targeting functions of the nano-particles are enhanced. The nano-drug has good effects in vitro and vivo and accordingly has a good application prospect.