Ideal drug delivery systems are required to be stable in circulation, while instable at targeted sites to induce a rapid drug release. To address this dilemma, a novel light cross-linkable and pH de-cross-linkable micelles were developed as drug nanocarriers. Poly(ethylene glycol)-poly-(hydrazone umbelliferone)-aspartamide (mPEG-OMC) with light responsive coumarin moieties and pH responsive hydrazone groups in the side chains was synthesized. The polymers can self-assemble into micelles, which can be conveniently stabilized via UV-light induced cross-linking based on the dimerization of coumarin moieties. While under slight acidic conditions, the cross-linked micelles can also be de-cross-linked by the cleavage of hydrozone bonds in the cross-linking segments, accelerating the release of encapsulated drugs. Thus the benefits of pH and light stimuli-responsiveness can be combined and their disadvantages are avoided. The Doxorubincin-loaded micelles showed high mortality towards HepG2 cells. We demonstrated the UV light cross-linkable micelles with pH-triggered de-cross-linking property as a new approach of designing smart drug delivery systems.