To improve the imaging quality of long-distance turbid underwater off-axis holographic imaging under the background of sparse ballistic photons and strong scattered light, this study proposes an underwater scattering imaging method based on off-axis digital holography. This method combines a spatial filtering device and the free regulation of a reference light intensity. A 4F filtering system can effectively filter out numerous scattered photons generated in the reflection process, thus significantly reducing the scattering noise, as well as improve the coherence of ballistic photons and optimize the imaging effect. Compared with the direct-imaging effect, the imaging distance of underwater scattering imaging with the 4F filtering system increases by 45.31% (attenuation length increases from 6.4 to 9.3). Additionally, by finely adjusting the intensity of the reference light, the effect of coherent noise can be reduced, while the image contrast and the accuracy of the reconstructed image can be improved. The structural similarity index measure (SSIM) of the reconstructed image generally increases by 0.05 to 0.13, and the peak signal-to-noise ratio (PSNR) generally increases by 0.5 dB to 2.4 dB. The proposed underwater scattering imaging method based on off-axis digital holography can increase the maximum imaging distance to 10.3. The SSIM value of the object reconstruction image is 0.175, the PSNR is 4.65 dB, and the RMSE is 164.23. After denoising by the neural network, the best imaging results are as follows: SSIM = 0.377, PSNR = 7.68 dB, and RMSE = 112.74. The proposed method provides an effective technique for long-distance turbid underwater scattering imaging.