Powder metallurgy technology has numerous advantages over classical metallurgy. However, in the production of parts by powder metallurgy technology due to a process consisting of pressing the powdered material in a mold which is then heated to the appropriate temperature in a certain time interval, residual porosity occurs in the finished product. Therefore, this master's thesis discusses the influence of the microstructure of sintered steel on its fatigue behavior under conditions of high-cyclic fatigue. The material considered is sintered steel Astaloy Mo+0.2C. The methodology of numerical modeling of material fatigue and the constitutive behavior of heterogeneous materials is explained in detail. Based on the metallographic testing, a representative volume element (RVE) was determined, which statistically represents the microstructural behavior of the heterogeneous material. Furthermore, the linear-elastic characteristics of the sintered steel ferrite matrix were determined using homogenization on a predefined RVE, which served as a basis in the assessment of high-cyclic fatigue. Numerical simulations were performed in the software package Abaqus. After determining the linear elastic behavior, the fatigue characteristics of the Astaloy Mo+0.2C ferrite matrix were determined by explicit consideration of the material microstructure. During determination the fatigue characteristics of the ferrite matrix under conditions of high-cyclic fatigue, two cases were considered: without the influence of medium stress and with consideration of the influence of medium stress according to Goodman. Numerical simulations of fatigue behavior were performed in the software package fe-safe. Unfortunately, experimental study of the mechanical properties of Astaloy Mo+0.2C has not been fully performed due to the consequences caused by the Covid-19 coronavirus pandemic. Therefore, it was not possible to validate the results of numerical simulations, while the material characteristics necessary for the conduction of numerical analyzes were taken from the literature.