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<i>Haemonchus contortus</i> poses a severe hazard to the healthy development of the sheep industry and threatens the welfare of sheep. Ivermectin is the primary anthelmintic used for the prevention and treatment of <i>H. contortus</i> parasitism. However, the widespread and uncontrolled application of ivermectin has resulted in the development and spread of resistant strains of <i>H. contortus</i>. P-glycoprotein (P-gp) plays important roles in the pharmacology and toxicology of ivermectin, and changes in <i>P-gp</i> expression levels can be used to analyze the resistance of <i>H. contortus</i> to ivermectin. This study aimed to analyze the effects of ivermectin on <i>P-gp</i> expression in <i>H. contortus</i> L3 larvae isolated from China and to evaluate whether changes in <i>P-gp</i> expression levels can be used to analyze resistant <i>H. contortus</i> strains. In the absence of drug treatment, the ivermectin-resistant strains isolated in China showed increased expression of <i>P-gp</i>11 (<i>p</i> < 0.01) compared with sensitive strains from elsewhere, whereas the expressions of <i>P-gp</i>2 and <i>P-gp</i>9.1 were downregulated (<i>p</i> < 0.01). When the same strain was compared before and after drug treatment, obvious differences in expression were observed between the different strains. Ivermectin-induced <i>P-gp</i> expression was found to be very complex among the L3 larvae of different strains. In addition, it was confirmed that using <i>P-gp</i> to determine ivermectin resistance in <i>H. contortus</i> strains from different geographic environments can yield different results.