A special compression device was devised to investigate the relation of resistivity and tightness of fiber assembly. The experimental results show that resistivity of loose fiber assembly can reflect the tightness among fibers in fiber assembly, and also show that tightness in cross-section horizontal to compression direction and that in cross-section vertical to compression direction have difference. A new parameter defined as the degree of fiber orientation in loose fiber assembly is proposed to characterize this difference. It can be expressed by that the degree of fiber orientation shows the 1/(3+C)th power dependence with respect to the ratio of resistivity in compression direction to that in the direction vertical to compression direction. From the experimental results, fiber orientation degree increases with increase of density of fiber assembly at the same fiber assembly weight. It increases with the decrease of fiber assembly weight at the same density of fiber assembly. From experimental results, parameter fiber orientation degree in loose fiber assembly and filling ratio can describe the compactness of loose fiber assembly comprehensively.