In this study, three-dimensional laser scanning technology was employed to measure geometrical data of the human spine vertebrae. Based on the measured point-cloud data of the vertebra figuration, a detailed three-dimensional nonlinear finite element model of the lumbosacral joint L5-S1 of the spine was created and used to investigate the biomechanical properties of the lumbosacral joint. The finite element model was finely developed and validated according to available experimental results. The results show that facet articulations are important to stability of the lumbosacral joint. 1000N compressive force or 100N anterior force may yield the facet joint slippage for around 1mm and the facet contact surfaces may slip for around 2.8mm under both of 10Nm extension moment and 1000N compressive force. The finite element model might provide a detailed and accurate computational model for biomechanical analyses of the lumbosacral joint and studies of relative instrument implant and individual design of instruments.