Controlled trials assessing quadratus lumborum block (QLB) for post-operative analgesia in hip surgery are scarce. This study aimed to compare ultrasound-guided QLB and lumbar plexus block (LPB) for clinical efficacy in hip arthroscopy. Patients undergoing hip arthroscopy in Beijing Jishuitan Hospital in January–June 2019 were randomized to the lumbar plexus (L) and quadratus lumborum (Q) groups (n = 25/group). After either ultrasound-guided block for 30 min, both groups were prepared for surgery after muscle strength measurement in the affected limbs. Opioid doses for patient-controlled analgesia (PCA), visual analog scale (VAS) scores in the resting and active states, upon leaving the post-anesthesia care unit (PACU), and at 2–48 h post-surgery were recorded, and post-operative complications were also recorded. Muscle strength in the affected limbs was significantly higher in the Q group compared with the L group (4.0 versus 2.0, P < 0.001). VAS scores were similar in both groups post-surgery (P > 0.05). One patient had epidural spread in the L group, with no other complications. Compared with ultrasound-guided LPB, ultrasound-guided QLB provides similar and good post-operative analgesia after hip arthroscopy, with less impact on muscle strength and fewer complications. These results should be confirmed in larger trials.