Abstarct: The need for various construction projects has usually caused problems such as settlement or shortage of load bearing capacity for civil engineers. Among the measures taken to stabilize the soil is the use of a variety of improvement methods. One of these applications is the use of micropile or small pile as a structural element in soil. In this research and in a laboratory program, after design and construct of a large-scale physical modeling apparatus, multiple static strain- control loading tests with a displacement rate of 10mm / min were performed to examine various factors such as length, diameter and slenderness ratio of micropiles in soils with different relative densities. In this study, SPSS software was used to analyze the results and determine the quantitative effect of parameters and EPR genetic algorithm-baxsed method was used to predict the behavior of micropiles. The length sizes of the used micropiles are 0.5, 0.75 and 1 meter and the diameter sizes of them are 1, 2, and 3 inch. The soil used is standard Firoozkooh sand, which is used in relative densities of 30% and 90%. The results of the study, in addition to confirm the performance of the device and accuracy of its results, show an impact of the diameter parameter approximately 1.1 times of the length at different densities, the effect of the density parameter 2.1 times of the diameter in different lengths and the effect of the density parameter 2.3 times of the length in different diameters. Finally, it is observed that EPR model has high accuracy in prediction and baxsed on SPSS results, density, diameter and length are respectively the most important parameters in assess and evaluate the amount of load bearing capacity in micropiles.