Relative methods, which are performed with the assistance of reference materials, are widely used in photon activation analysis(PAA). On the contrary, absolute methods, which are conducted without any reference material, are rarely applied due to the difficulty in obtaining photon flux. To realize absolute measurement in PAA,we retrieve photon flux in the sample via Monte Carlo simulation and raise a novel procedure—quasi-absolute method. With simulated photon flux and cross section data from existing databases, it is possible to calculate the concentration of target elements in the sample straightforwardly. A controlled experiment indicates that results from the quasi-absolute method for certain elements are nearly comparable to relative methods in practice.This technique of absolute measurement has room for improvement in the future and can serve as a validation technique for experimental data on cross sections as well. Relative methods, which are performed with the assistance of reference materials, are widely used in photon activation analysis (PAA). On the contrary, absolute methods, which are conducted without any reference material, are rarely applied due to difficulty in obtaining photon flux To realize absolute measurement in PAA, we retrieve photon flux in the sample via Monte Carlo simulation and raise a novel procedure-quasi-absolute method. With simulated photon flux and cross section data from existing databases, it is possible to calculate the concentration of A controlled experiment that that results from the quasi-absolute method for certain elements are nearly comparable to relative methods in practice.This technique of absolute measurement has room for improvement in the future and can serve as a validation technique for experimental data on cross sections as well.