Statistical methods were employed to study the structure characteristics of sisal fibers. Two types of fiber surface treatment methods, namely chemical bonding and oxidization were used to improve the interfacial bonding properties of sisal fiber reinforced HDPE (sisal/HDPE) composites. Interfacial properties were evaluated by single fiber pull out test. The interfacial shear strength (IFSS) was calculated and analyzed by the statistical parameters. The results were compared with those obtained by traditional ways. A novel method which could more accurately evaluate the interfacial properties between natural fiber and polymeric matrices was proposed.