Abstract: Nuclear magnetic resonance(NMR) logging can be directly used to determine the properties of the reservoir fluid.But it is affected by instrument parameters of pre-logging and the characters of the fluid itself.In this paper,the influences of echo spacing(T_E),wait time(T_W),oil saturation and salinity of formation water on the T₂ spectrum shapes and the transformation rules were discussed based on the experiments of cores with different porosities acquired from different oilfields.The experimental results indicate that if the parameter T_E is selected illogically,the NMR spectrum will lose some reservoir information and decrease the resolution capability to the short relaxation components.Different T_W results in different fluid polarization,and the variation in the oil saturation and formation water salinity have different responses on T₂ spectrum shape.Therefore,the influence on T₂ spectrum of these factors should be considered in NMR logging data processing and interpretation.