In this work, magnetic FeO/FeO nanocomposites were prepared via a novel rapid combustion process. The silica was precipitated on the surface of FeO/FeO nanocomposites. The silica-coated magnetic nanocomposites were cross-linked with glutaraldehyde, on which cellulase was covalently immobilized. The morphology, composition, and property of the prepared nanomaterials were characterized by the scanning electron microscopy (SEM), the energy dispersive spectrometry (EDS), the X-ray diffraction (XRD), the vibrating sample magnetometer (VSM), and the Fourier transform infrared (FTIR) spectroscopy. The immobilization conditions were optimized by varying operating parameters and determined to be 0.05 mL of 0.5% cellulase solution for 2 h. The catalytic stabilities of the immobilized cellulase were evaluated. The results showed that the immobilized cellulases performed higher apparent activity at pH 4.5 and exhibited good thermal stability compared with their free counterparts. The Michaelis-Menten equation showed that K and V of free cellulase were 3.46 mol·L and 0.53 mol·min, respectively. The immobilized cellulase had higher K and V (18.99 mol·L and 0.59 mol·min). The retained activity of the immobilized cellulase maintained over 71% of the initial activity after being used for five cycles.