The oil-water relative permeability is a key parameter to characterize the effect of water injection in low permeability oil reservoirs. Due to the narrow pore size and large seepage resistance of low permeability reservoirs， the “end effect” of core leads to the inconsistency between the calculated oil-water relative permeability curves and the actual results， which affects the establishment of water injection development scheme of low permeability reservoirs. To avoid the influence of core “end effect” on the relative permeability， the CT scanning has been applied to monitor the in-situ water saturation profiles along the low permeability core at different time points. Based on the experience formula of oil-water relative permeability curve， optimal parameters of the relative permeability has been obtained by combining the oil-water flow methods in low permeability reservoirs， and the simulated annealing optimization theory. The results show that CT scanning test is a very effective test method which can not only monitor water saturation profile and water saturation characteristics in the central core， but also avoid the influence of “end effect”. The global optimal relative permeability curve has been obtained with the Simulated Annealing method. The test results of water saturation and the pressure difference at both ends of the core accord with the results of calculation. This method has the advantage of high goodness of fit and satisfactory effect， with the relative permeability less than 8%. This method is proved to be efficient and accurate for calculating oil-water relative permeability curves， providing a strong support and guidance for the development of low permeability reservoirs.