Abstract: Long-acting analgesia is a common clinical treatment method after surgery. The slow-release injection with long-acting analgesia has the advantages of less medication frequency and stable effect. In this study, the analgesic drug lappaconitine hydrobromide lyotropic liquid crystal injection was prepared, and its sustained release mechanism, drug release and pharmacodynamic characteristics were evaluated. The results of polarizing microscope and freeze-transmission electron microscope showed that the lyotropic liquid crystal injection of the liquid crystal precursor preparation of lappaconitine hydrobromide could be obtained by the combination of glycerol monooleate (GMO) and soybean lecithin (SPC) in different proportions. The results of dissolution study in vitro showed that the drug release rate of different forms of liquid crystal preparations was layered liquid crystal > cubic liquid crystal > hexagonal liquid crystal. The mathematical model fitting results of the release data showed that the external release of layered liquid crystal, cubic liquid crystal and hexagonal liquid crystal conforms to the Ritger-Peppas model, and the release mechanism was Fick diffusion. The results of pharmacodynamics study in vivo showed that the analgesic effect of lappaconitine hydrobromide lyotropic liquid crystal injection lasted for 3 days, and there was no abnormality in the incision and local tissue, showing good safety and tolerance. The study on drug release and elimination process of the in vivo gel repository showed that lappaconitine hydrobromide could be completely released from the lyotropic liquid crystal 3 days after administration, and the sustained-release materials could be gradually eliminated locally. All animal experiments were approved by the Experimental Animal Ethics Committee of the Shanghai Institute of Materia Medica, Chinese Academy of Sciences (No. 2021-08-GY-61) and the experiments were conducted in accordance with the relevant guiding principles and regulations. The lyotropic liquid crystal injection of lappaconitine hydrobromide prepared in this study presented a solution state at room temperature, and underwent phase transition in contact with the body fluid at the administration site, formed a drug depot and exerted a slow drug release effect. This preparation can reduce systemic toxicity, prolong the duration of analgesia, reduce the number of administrations, improve the compliance of postoperative patients, and provide a reference for the design of long-term sustained release analgesic preparations.