Organic near-infrared (NIR) photosensitizers (PS) largely facilitate photodynamic therapy (PDT). To overcome aggregation induced quenching and diminishment of reactive oxygen species (ROS) generation capability of NIR-PS, aggregation-induced emission (AIE) effect groups have been introduced to generate NIR AIE photosensitizers. However, currently reported NIR AIE photosensitizers all take "always-on" activity that may cause systemic phototoxic side effects. Tumor microenvironment activatable NIR AIE photosensitizers have not been reported. Here we develop an activatable NIR AIE PSnanoparticle (a-NA-PSNP) for near-infrared-II (NIR-II) fluorescence (FL) imaging-guided PDT under 808 nm excitation. NIR AIE photosensitizer (N-PS) is designed and frames with cysteine (Cys)/glutathione (GSH) responsive charge transfer complex (CTC) in bovine serum albumin (BSA) to obtain a-NA-PSNP. With the aggregated state in BSA, N-PS shows high quantum yield with good photostability. As an energy acceptor, CTC quenchs NIR-II fluorescence and ROS production capability of a-NA-PSNP in normal cells and tissues. CTC is decomposed in response to tumor microenvironment Cys/GSH, therefore recovers NIR-II fluorescence of a-NA-PSNP and efficiently generates ROS under 808 nm light irradiation. The depletion of Cys/GSH also regulates tumor intracellular reductive environment to further facilitate PDT. Both in vitro and in vivo results confirmed the tumor microenvironment selective and efficient activation of a-NA-PSNP, indicating its potential in cancer therapy.