We investigated the dose-effect relationship of photosensitizer ZnPc in photodynamic therapy (ZnPc-PDT) in killing the U87 MG cells and provided reference for rational administration of ZnPc. The proliferation of U87 MG cells was determined by MTT (thiazolyl blue tetrazolium bromide) tests. The effect of ZnPc concentration, laser power density, exposure time, oxygen content and tissue thickness on the proliferation was investigated. Then the production of singlet oxygen during ZnPc-PDT was determined by the DPBF probe and DCFH-DA reactive oxygen species assay kit. The cell morphology and the proportion of cell death was observed by an inverted microscope. The results show that U87 MG cell viability changes different parameters setting after ZnPc-PDT, and we can get a good ZnPc-PDT effect by adjusting the parameters.