A FEM analysis for studying mixed-mode fracture problem of chopped strand mat glass fibre reinforced polyester laminate is presented. The analysis is formulated on the basis of 8-node quadrilateral isoparametric element. The collapsed triangular quarter-point singular elements were used for calculating stress intensity factors KI and KII. The crack propagation process was computed by implementing constraint release technique. Three different approaches to the solution of stress intensity factors KI and KII were compared. The effect of constraint condition imposed upon the displacement of the three collapsed nodes of the crack tip elements on the KI and KII results was evaluated. The mixed-mode critical stress intensity factors KIC and KIIC were estimated for CSM-GRP through the consideration of KI and KII calculated and the measured failure load and critical crack length in the experiment.