Purpose: To investigate the optimal adaptive statistical iterative reconstruction (ASIR) percentage in monochromatic level combined with spectral computed tomography imaging for improving abdominal image quality. Methods: The monochromatic images at 55 and 70 keV in 32 patients with abdominal diseases at arterial and venous phases, noise, contrast-to-noise ratio (CNR) and subjective scores of image quality were analyzed. The reconstruction imaging was performed at 0%, 30%, 50% and 70% ASIR for the arterial and portal venous phases in the tested group. The data of these images were analyzed after a total of le sets of data were reconstructed at 70 keV and 55 keV energy points with different ASIR percentages. Results: In 50 and 70 keV, the noise was significantly decreased with increase of ASIR percentage. In 70 keV, the liver CNR in the arterial phase and the pancreatic CNR in both phases were significantly greater in 70% than in all the other percentage ASIR. The artifacts were significantly fewer in the 30%, 50% and 70% ASIR than in the 0% ASIR, and also fewer in 30% ASIR than in 70% ASIR in both phases. The diagnostic confidence was significantly greater in 30% and 50% ASIR than in 0% and 70% ASIR in the arterial phase and was significantly greater in 30%, 50% and 70% ASIR than in 0% ASIR in the venous phase. In the 55 keV, the left kidney CNR was significantly greater in 50% or 70% ASIR than in 0% or 30% ASIR, and the venous phase pancreatic CNR was significantly greater in 70% ASIR than in 0% or 30% ASIR. The vessel images were significantly better in the 50% than in the all other percentage ASIR. Conclusion: This study shows that 70 keV plus 30% ASIR and 55 keV plus 50% ASIR are the optimal protocol which can improve the image quality of the abdominal organs and blood vessels.