From a series of in-soil creep test, it has been found that the deformation and strain increment of geogrid due to creep is concentrated in the vicinity of pull-out opening. Based on the comparison between calculated in-soil creep deformation behaviors by using the method proposed in this paper and those observed by in-soil creep test, it has been pointed out that it is important to construct a reinforced soil structure so that sufficient frictional resistance develops between soil and geogrid. The importance of the establishment of design method considering the overall deformation of the reinforced soil structure due to the in-soil creep deformation of geogrid has also been pointed out.