The work was focused on modelling of cracks and simulations of their propagationin timber beams. The aim was to find out the influence of flaws on load-carrying capacity. Inbeam design and beam inspection, it is necessary to determine the load-carrying capacity of abeam with flaws. There is not much information in literature about the influence of flaws onbending and shear strength of timber beams. Standards for fracture mechanics design approachfor timber structures are not easily available.The results from simulations of loaded timber beams with flaws are discussed in this paper.Two different types of timber beams were analysed. First type was a sawn timber beam andfor that four different models were analysed: first model was a beam without flaw; secondmodel was a beam with a straight central flaw; next was a beam with an oblique crack andfourth beam had a round hole in the middle of the span. Second type of beam was a gluedlaminated timber beam (glulam). For this type, five different models were analysed. First fourvariants were the same as for the solid timber beam and the fifth variant had an initial crackalong a glue line. We analysed these types of flaws, since they are the most common flaws inwood.Simulations were conducted in ABAQUS. Material properties of wood used in the modelswere retrieved from standards; C24 for solid timber and GL24c for glulam timber beams.Dimensions of beams were the same for all variants and beams were considered simply supported.For an analysis of crack propagation, linear elastic fracture mechanics was considered.Modelling fracture was conducted using the extended finite element method (XFEM).The energy approach was used for the analysis of crack propagation. Comparing results forsolid and glulam beams with and without cracks gave us an overview how different flaws influenceload-carrying capacity of the beams and under which loading failure occurs. Simulatingtimber beams is more complicated compering to steel or plastic. By understanding how tosimulate flaws in wood material it is possible to obtain reliable results with finite elementanalysis