Defibering processes of 3 plantation building use species used for manufacturing medium density fiberboard(MDF) were investigated and appropriate refining plate pattern was determined. Experimental conditions were as follows: 1)species were Chinese fir(Cunninghamia lanceolata),loblolly pine(Pinus teada)and slash pine(Pinus elliottii); 2)3 refining plate patterns were classified as mediumfine,medium and coarse; 3)chips were steamed under fixed pressure of 0.40.65MPa for 3,6,9 and 12 min respectively; 4)refining plate gap was adjusted to about 0.1mm.Experiment results showed: mediumlong fibers(retained on 32115 mesh) content was 50%70%,but medium plate pattern produced better fiber, cooking time had no significant effect on fiber quality and internal bond so that 3 min was enough for cooking.