The change ofQ-band fluorescence lifetime of tetraphenyl porphyrins(TPP) adsorbed on the surface of silver nanoparticles is reported. The lifetime was extended when the surface plasmon resonant peak of silver nanoparticles was adjusted to resonant with theQ- absorption band. Silver nanoparticles bring large surface plasmon resonant enhancement effect to the surface light field, and the excited TPP molecules have higher polarity. The enhanced light field will stabilize the TPP molecules of high polarity, which causes the extendedQ-band fluorescence lifetime. It has an important significance in photodynamic therapy using porphyrins as photosensitizer.