Abstract: In this paper,the reinforcing effect, the stretching and compressing destructive mechanism in the polyurethane foam plastics reinforced by short cutting glass fibres have been studied. The results show that the reinforcing effect is best when the fibre length is 12 mm and the fibre content is 6 wt%. The stretching intensity, the compressing intensity and the compressing modulus are increased by 75%, 25% and 30%, respectively. When the foam reinforced by fibres is stretched, the cracks are produced and the cracks spread. They may stop spreading (as the stress is low) or may present deflection (as the stress is high) when the cracks meet fibres. Different destructive shapes (the fibres are pulled out, broken and so on) may occur when the foam is destroyed. The prop of the foam structure may be crooked, twisted and out of shape when the foam reinforced by fibres is compressed destructively. It leads to rupture of foam wall, losing stability of prop and destruction of material.