Nanostarch has attracted much research interest recently due to its biodegradability and biocompatibility. A type of biocomposite film based on corn nanostarch (CNS) as the matrix and cellulose nanocrystals (CNC) as the reinforcement was prepared using a solution casting method. The influences of corn nanostarch concentration (CCNS), glycerin dosage (Dg), and cellulose nanocrystals dosage (DCNC) on the tensile strength of the biocomposite film were investigated by central composite design. The results were examined by an analysis of variance (ANOVA) and response surface methodology (RSM). The optimized process conditions as follows: CCNS of 11.25%, Dg of 12.00%, and DCNC of 5.00%. The CNS/CNC biocomposite film produced under these conditions showed a high tensile strength of 12.90 MPa. The CNS/CNC biocomposite film was characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), water contact angle, and scanning electron microscopy (SEM). The CNS/CNC biocomposite film has potential application prospects in the field of food and biomedical packaging.