The invention relates to a pH-sensitive drug-loaded particle as well as a preparation method and application thereof. The drug-loaded particle is prepared by the following steps: dissolving camptothecin or a camptothecin derivative in an alkaline aqueous solution, adding a low-anticoagulant heparin modifier and ultrasonically processing so as to obtain a mixed solution; and conducting millipore filtration on the mixed solution, so that the drug-loaded particle is obtained. The drug-loaded particle, under slightly acid conditions, such as at pH value of 1.5-6.0, is under a gel state; the grain size of the gel is 1-3 [mu]m; and the gel, in the acid tissues of a human body, can be degraded to release the camptothecin or the camptothecin derivative, so that an anti-tumor effect is achieved.