OBJECTIVE： To investigate the effects of multidrug resistance gene 1（MDR1） C3435T polymorphism on the dose of  analgesia agents （dezocine combined with sufentanil） after joint replacement. METHODS： 300 patients receiving joint replacement were selected from Tianjin People’s Hospital and Tianjin Port Hospital during Jan. 2014-Feb. 2016. They were given dezocine and sufentanil for postoperative analgesia. PCR-RFLP was used to determine MDR1 C3435T polymorphism； VAS scores， Ramesy scores， the dose of dezocine+sufentanil and the occurrence of ADR were compared among different genotypes. RESULTS： Among 300 patients， there were 100 （33.3％）， 102 （34.0％） and 98 （32.7％） cases of MDR1 C3435T CC， CT and TT genotype， respectively， the frequencies of which were all in line with Hardy-Weinberg balance （P＞0.05）. There was no statistical significance in VAS scores and Ramesy scores among different genotypes 0， 24， 48 h after surgery （P＞0.05）. No excessive sedation was found. The dose of dezocine+sufentanil in CT and TT genotype were all significantly lower than CC genotype 0-24 h， ＞24-48 h after surgery， with statistical significance （P＜0.05）. There was no statistical significance in drug dose between CT and TT genotype during above periods （P＞0.05）. The incidence of postoperative nausea and vomiting （PONV）， ADR in TT genotype were significantly lower than CC and CT genotypes， with statistical significance （P＜0.05）. There was no statistical significance in the incidence of PONV and ADR between CC genotype and CT genotype， and in the incidence of itch among different genotypes （P＞0.05）. CONCLUSIONS： With similar sedation and analgesic effect， MDR1 mutant type have lower resistance to dezocine+sufentanil， and smaller drug dose is need， the incidence of ADR is lower. MDR1 genotype can be regarded as an important indicator of clinical individualized treatment.