Background Robot-assisted laparoscopic radical prostatectomy ( RALRP) has better effects than conventional laparoscopic radical prostatectomy (LRP). However, limited data is available regarding the incidence and risk factors for developing postoperative delirium in patients undergoing these two procedures. This study aimed to assess the incidence of postoperative delirium in patients undergoing RALRP and LRP, and evaluated the risk factors for developing postoperative delirium Methods From June 2013 to December 2019, 81 cases of RALRP patients and 71 cases of LRP patients were included in this study. The unpaired Student t tests, repetitive measure analysis of variance and chi-square test were used to compare several different parameters. The binary logistic regression analysis was used to explore the independent risk factors of postoperative delirium . Results The incidences of postoperative delirium in group RALRP and LRP were (17.3% VS 32.4%, P = 0.03), IAP was (12.72 ± 1.87 VS 13.37 ± 1.12 mmHg; P = 0.01), PaCO2 at post-pneumoperitoneum and after loosening pneumoperitoneum were (47.89 ± 10.89 VS 38.65 ± 16.32 mmHg; P < 0.001; 40.77 ± 5.34 VS 43.57 ± 4.54 mmHg; P = 0.001), the overall cost was (8.29 ± 5.55 VS 5.18 ± 1.51 Ten thousand RMB, P < 0.001). The incidence of postoperative delirium increased 1.17 times, 1.13 times, and 1.66 times for each unit increase recovery time (Tr), post-pneumoperitoneum PaCO2 and IAP. Conclusion The RALRP group had a lower IAP, lower incidence of postoperative delirium and shorter recovery time compared with the LRP group, but the overall cost was higher. IAP was the main factor affecting the incidence of postoperative delirium.