Abstract: Fast growing poplar wood was modified with low molecular phenol-formaldehyde resin (PF) by means of full cell vacuum method. Mechanical properties of modified and untreated poplar woods were analyzed from the point of reliability. The results showed that the modification method was effective to increase the mechanical performance of the stuff, for that its modulus of elasticity, modulus of rupture and longitudinal compression strength increased by 87.784 %, 22136 %, and 207.358 %, respectively after treatment with PF. The reliability extent of materials strength was put forward, indicators were set modulus of elasticity, modulus of rupture and compress strength respectively, and these indicators could meet normal distribution better.