By using the spatial filtering method and the oceanic turbulence power spectra, the numerical simulation program of imaging by diffuse reflection light from extended objects in oceanic turbulence is designed. The dependence of the imaging quality on the oceanic turbulence parameters and the receiver size is studied. It is found that, with the increases of the ratio of seawater refractive index change caused by temperature to that caused by salinity in the oceanic turbulence power spectra and the dissipation rate of seawater temperature variance, and with the decrease of the dissipation rate of kinetic energy per unit fluid mass, the seeing parameter in oceanic turbulence decreases and the imaging quality degrades. The proposed numerical simulation method provides a feasible and correct approach for the study of imaging by diffuse reflection light from extended objects in oceanic turbulence.