The development of more efficient photosensitizers with minimal damage to surrounding normal tissues has been a valuable and challenging subject during photodynamic therapy (PDT). Herein, a stimuli-activated porphyrinic photosensitizer (PEG-TPP-DNB; PEG = poly(ethylene glycol); TPP = 5,10,15,20-tetraphenylporphyrin; DNB = 2,4-dinitrobenzene) with capabilities of fluorescence and, remarkably, singlet oxygen quenching was prepared successfully for photodynamic therapy with high efficiency and biosecurity. The amphiphilic PEG-TPP-DNB could be self-assembled into nanomicelles in aqueous media and dissociated in response to reductive thiol such as glutathione. Meanwhile, the fluorescence and singlet oxygen generation of porphyrinic photosensitizer would be activated to regenerate. Moreover, the intracellular uptake and localization effectively confirmed the redox-responsive and activated behavior of PEG-TPP-DNB micelles. The cytotoxicity in vitro revealed that the micelles had low dark toxicity and great phototoxicity, and in vivo bioimaging and antitumor evaluation further indicated that the micelles possessed selective tumor imaging and targeted PDT antitumor effect as well as low systemic toxicity. Overall, this tumor microenvironment-activated photosensitizer system may provide a useful strategy for precise photodynamic therapy.