3-hydroxyflavor(-3HF) is an organic molecule with excited-stated proton transfer(ESPT) effect.The ESPT process of3-HF was investigated by using two photon fluores-cence technique.Using open apertureZ-scan technique,we measured two photon absorp-tion coefficient of-3HF which was excited by the picosecond pulse laser at532nm,and ob-tained the two photon absorption coefficients of3-HF under different light power,the resutls have showed that two photon absorption coefficient of3-HF decreases as the light power increases.Excited by the picosecond pulse laser,many molecules of3-HF is excited to the excited state and can not be back immediately to the ground state,the amount of3-HF mol-ecules in the ground state are decreased,so the two photon absorption coefficient of3-HF will be decreased when the light power increases.