The loess in the Lishan piedmont fault zone in Lintong District of Xi'an City was studied with fiber-reinforced treatment. The dynamic triaxial tests of reinforced loess were carried out based on the orthogonal test plan. The difference of dynamic elastic modulus of fiber reinforced loess was discussed, and the influencing factors were compared and analyzed. Through the range analysis of the orthogonal test results, it is concluded that the fiber length, fiber content, and soil saturation are the three major factors affecting the dynamic elastic modulus of fiber reinforced loess, with an order of soil saturation, fiber length, and fiber content. The results of variance analysis show that the significant levels of soil saturation on glass fiber reinforced loess and polypropylene fiber reinforced loess are 0.035 and 0.058, respectively, indicating that the soil saturation has a prominent effect on the dynamic elastic modulus of fiber reinforced loess. The optimal levels are 0.6% fiber content, 50% soil saturation, and 12-mm fiber length for both the glass fiber reinforced soil and polypropylene reinforced soil. The results also show that the dynamic elastic modulus of the two reinforced loess is about 1.5 times that of fiber-free conditions. There is a positive correlation between the fiber length and the dynamic elastic modulus of reinforced loess. Both the dynamic elastic modulus of glass fiber reinforced loess and polypropylene fiber reinforced loess increase first and then decrease with the increase in fiber content. The fiber reinforced treatment of loess is helpful to improve the strength of loess and ensure the safe construction and operation of engineering foundation in the fault zone.