In order to process underwater imaging to the best possible level, an imaging model based on beam propagation was established. The presented model included not only the laser beam propagation affected by absorption and scattering, but also the effects of underwater turbulence and the diffraction limit of sensors. By this model approximately quantified optical transfer functions (OTFs) were studied. Thus, under this framework, the approaches of image enhancement, restoration and super-resolution reconstruction (SRR) can be extended by incorporating underwater optical properties based on OTF or point spread function (PSF) of the imaging system. Experimental results proved that the imaging range and the image quality can be effectively enhanced, which are critical in underwater imaging or detecting.