A two-phase route was developed to form a new theranostics-based system. The comb polymer poly (glycidyl methacrylate)-graft-ethane diamine-graft-polyethylene glycol (PGMA-g-EDA-g-PEG) was used to modify the quantum dots (QDs) by the method of ligand exchange. Subsequently, due to a large amount of amino groups on the surface of QDs, the doxorubicin (DOX) was conjugated by amine bonds to form pH-sensitive drug release system. UV-vis transmission spectra and PL spectra showed that the nanoparticles maintained the optical properties of QDs and DOX. The transmission electron microscopy analysis indicated that QDs were well dispersed in water and still had small sizes (7 nm) after ligand exchange and conjugated with DOX. Then the thermogravimetric analysis (TGA) revealed that about 80 wt% comb-shaped polymers coated on the surface of QDs, and about 10 wt% QDs was in nanoparticles PGMA-g-EDA-g-PEG-QDs-DOX. In vitro release studies showed that PGMA-g-EDA-g-PEG -DOX and PGMA-g-EDA-g-PEG-QDs-DOX were pH sensitive. Findings from this study suggested that nanoparticles PGMA-g-EDA-g-PEG-QDs-DOX can be used in a new field combined both imaging and targeted therapy.