The factors of thickness variation control are further studied by means of statistical analysis. The results indicated, the thickness square deviation affected by the single species (Masson′s pine) as raw materials instead of the mixed and uncontrolled SPecies decreased by 79%, so the raw materials is one of the key factors of thickness variation control; when the correlation of thickness with weight of boards become insignificant after the forming quality has been improved, the thickness variation coused by hot press could be distinguished from the forming unit, and then the basis could be provided for putting further measures into effect. The final thickness variation of the unsanded particleboard can come up to the standards from Siempelkamp Co of Germany and meet elementary requirements of international market. The above results have confirmed the practicality and reliability of using statistical methods to diagnose the factors of thickness variation control in particleboard.