In this paper, the temperature and pre-crack effects on the delamination resistance of woven glass fibre reinforced polymer (GFRP) sandwich composites under Mode I loading was experimentally investigated and numerically modelled. For this purpose, the sandwich composite panel was fabricated with vacuum assisted resin infusion molding (VARIM). The mechanical properties were obtained at room and high temperature. Double cantilever beam (DCB) test was adopted for the measurement of delamination resistance by evaluating the strain energy release rate (SERR) value to obtain the fracture properties of woven GFRP sandwich composites. The three analytical methods, the experimental compliance calibration method (CCM), Modified Compliance Calibration Method (MCC) and Modified Beam Theory (MBT) have been used. In the finite element analysis virtual crack closure technique (VCCT) was used. The results obtained from 3D finite element analysis for various delamination lengths compare well with the experimental results. It is seen that there is an agreement between experimental and numerical results so that VCCT analysis is to be an appropriate method for analysing a SERR value of sandwich composites.