Terahertz (THz) digital holographic imaging is one of the frontier research directions of terahertz imaging technology, the resolution is the key of this field. Most studies of digital holographic resolution are based on the classical resolution estimation, namely the two-point resolution, and rarely involve the single point resolution. Within an inverse problem framework, by comparing and analyzing the results of the single point resolution of terahertz on-axis digital holography in different detector parameters, the change in the resolution of each point on the object plane and the spatial distribution of single point resolution are given intuitively with the change in duty cycle, pixel number and other detector parameters. The results are of great significance to the optimization of detector parameters in practice and evaluating the improvement of the THz digital holographic resolution.