Poplar fibers and phenolic resin were used to prepare high density fiberboard（HDF） with different densities and resin contents. The mechanical properties, thickness swelling and water absorption properties were tested. The effects of density and resin content on mechanical properties, water resistance and microstructure of HDF were explored. The results showed that with the increase of density and resin content, the thickness swelling and water absorption of HDF decreased, while the mechanical properties of HDF increased. When the density was at 1.1 g/cm3 with a resin content of 10%, the water resistance and mechanical properties of the board reached the optimum respectively. The mechanical properties of the prepared fiberboard met the strength requirement of GB/T 31765 — 2015 High Density Fiberboard（HDF-GP HMR）.