Micro-pore structure is complex of ultra-low permeability sandstone reservoir, and occurrence condition of fluid is different from conventional reservoir. Movable fluid variation characteristics and diversity origin of samples in Yanchang group of Ordos basin are analyzed through NMR technology. The results show that pattern distributions are various, cutoff value of is moderate—high，parameters of movable fluid change greatly, movable fluid parameters of every formation present difference. Variation range of movable fluid parameters is large when permeability of sample is minor. The data points of movable fluid parameters converge and Variation range decrease with the increasing permeability. Physical property, pore (especially secondary pore) development and communication degree, microcrack development degree and occurrence mode and filling degree to pore of clay mineral are the main reason to cause deviation of movable fluid parameters. Parameters of movable fluid which are the integrated reflection on micro-feature parameters should be considered in the reservoir evaluation.