Non-uniform spatial resolution or axial blurring is a major limitation in conventional pinhole SPECT, which is largely attributed to incompleteness of the acquired projection data sets. Recently, we have experimentally demonstrated that the non-uniform spatial resolution could be improved by a new design of the pinhole orbit that satisfies the completeness of pinhole SPECT reconstruction (Tuy's condition). This study was intended to evaluate systematically the effect of our two-circular orbit system by a computer simulation and to examine an effective oblique angle about the additional orbit of two orbits. A numerical multiple-disk phantom with seven disks was used. Forwarded projection data without noise and with Gaussian noise were used to evaluate the axial spatial resolution uniformity and the statistical noise property, respectively. The angles of the additional orbit were chosen every 15° in the range from 0° to 75° for object's axis. Single and two-orbit data were reconstructed by 3D-OSEM method for pinhole SPECT. Our simulation showed two-orbit acquisition of any combinations was significantly effective for the improvement of both spatial resolution uniformity (81 - 93% at the edge disk of the phantom) and statistical noise property (69 - 88% at the edge disk of the phantom) compared with single orbit acquisition. Especially, combination of 90° and 60° orbits resulted in the best performance among other orbital combinations.