Biodegradable poly (β-hydroxybutyrate) (PHB)/poly (ε-caprolactone) (PCL) blends with different composition were prepared by melt mixing, the crystallization and mechanical properties of the blending system were studied, and the influence of cellulose and cellulose derivatives on the mechanical properties of the blending system was also investigated. The phase morphology of the blend material was observed by field emission scanning electron microscope (SEM), the influence of PCL on the spherulitic morphology of PHB was studied through the polarizing optical microscope (POM), the mechanical properties of PHB/PCL blend system were characterized by tensile test and impact test, the effects of cellulose and cellulose derivatives on the mechanical properties of PHB/PCL blend system were further studied. Studies have shown that PHB/PCL blend system is a typical thermodynamic incompatible system. PCL phase promoted the growth rate of PHB spherulite, with the increase percentage of PCL phase, spherulite growth rate of PHB was accelerated. The presence of PCL improved mechanical properties of PHB, the tensile strength of PHB/PCL70/30 system had increased by 20% compared with pure PHB. The impact strength of PHB/PCL blending system is 2 ~ 4 times higher than pure PHB. PCL improved the modulus and viscosity of the blend system. Cellulose materials further improved the tensile strength of the blending material.