Abstract: Objective To observe the influence of ultrasound guided transversus abdominis plane block on postoperative analgesic effect and immune function in elderly patients undergoing laparoscopic radical resection of rectal cancer. Methods Sixty elderly patients undergoing laparoscopic radical resection of rectal cancer were randomly divided into observation group and control group.Ultrasound guided transversus abdominis plane block after general anesthesia induction was performed in the observation group (intravenous injection of 0.25% ropivacaine hydrochloride of 30 ml), while the control group received intravenous injection of equal volume saline.The visual analogue score (VAS score) and related parameters of hemodynamics were observed before anesthesia (T0), 1 h after operation (T1), 12 h after operation (T2), 24 h after operation (T3) and 48 h after operation (T4).Twenty-four hours analgesia pressing times and total postoperative sufentanil were recorded.CD4₊%, CD8₊% and IFN_-γ levels and adverse reactions were compared between the two groups. Results Compared with the control group, MAP in the observation group decreased at T1 and T2, and HR decreased at T2 and T3 (P < 0.05).Compared with the control group, the VAS scores in the observation group were lower at T1, T2, T3 and T4;the postoperative 24 h pressing times and amount of sufentanil were decreased (P < 0.05).Compared with the control group, CD4⁺% levels in the observation group increased at T1, T2, T3 and T4, IFN_-γ levels at T2 and T3 were higher (P < 0.05).Compared with the control group, the incidence of adverse reactions in the observation group was lower (P < 0.05). Conclusion Ultrasound guided transversus abdominis plane block used in laparoscopic radical resection of rectal cancer in elderly patients has better postoperative analgesic effect, stable hemodynamics and less postoperative pain, and it has protective effect on immune function and lower the incidence of adverse reactions.