Objective To investigate the effects of ultrasound guided continuous adductor canal block (CACB) combined with periarticular local infiltration analgesia (PLIA) in the postoperative analgesia of children undergoing knee arthroplasty. Methods 78 patients undergoing unilateral knee arthroplasty in orthopedics department of our hospital from February 2016 to March 2018 were selected and divided into two groups according to the different anesthesia regimens. The observation group (n=38) received the ultrasound guided CACB combined with PLIA, while the control group (n=40) just received the ultrasound guided CACB. Then the pain degree assessed by the visual analogue scale (VAS), postoperative analgesia satisfaction, quadriceps strength, mobility of knee join and complications were observed in both groups. Results The analgesic satisfaction of the observation group was significantly higher than that of the control group at postoperative 6h, 12h and 24h (P＜0.05). The incidence rate of the quadriceps weakness of the observation group was significantly lower than that of the control group at postoperative 4h, 6h and 12h (P＜0.05). The VAS score of the observation group was significantly lower than that of the control group at postoperative 24h (P＜0.05), while no difference was found at postoperative 4h, 6h, and 12h (P＞0.05). The time of active straightleg raising and passive flexing knees to 90° in the observation group was shorter than that of the control group (P＜0.05). The overall incidence of complications in the observation group was significantly lower than that in the control group (5.3% vs 22.5%, P＜0.05). Conclusion The application of ultrasound guided CACB combined with PLIA can significantly reduce the VAS score, ameliorate the knee joint mobility, shorten the prognosis time and promote the outcomes for patients undergoing unilateral knee arthroplasty, which is worthy of promotion.