Background <p>The methods for assessing colonic transit in patients with functional constipation include the&#xa0;radiological method and Tc-99m scintigraphic method. This study aims to validate the practicality and accuracy of the Tc-99m scintigraphic method in evaluating colon transit, while also exploring the significance of the geometric center (GC).</p> Methods <p>Our study is a single-center, retrospective analysis. We examined the medical records of 47 patients, who underwent colonic transit by the Tc-99m scintigraphic method and the radiological method for investigation of chronic constipation. Geometric center (GC) and transmit index (TI) were calculated respectively in these two methods. The patients were divided into four types of constipation: normal transit constipation (NTC), slow transit constipation (STC), defecatory disorders (DD) and STC combined with DD.</p> Results <p>The results of the&#xa0;Tc-99m scintigraphic method and radiological method were consistent in the diagnosis of slow colon transmission (Kappa value = 0.718, <i>P</i> &lt; 0.001). TI and 48-h GC were positively correlated (r = 0.657, <i>p</i> = 0.001). Patients with DD exhibited higher 24-h GC and 48-h GC values compared to those with STC.</p> Conclusion <p>Tc-99m scintigraphic method can be used to evaluate colonic transit in patients with constipation, and GC values may be used to distinguish the types of constipation.</p>