Dendrobium officinale Kimura & Migo is an important medicinal and edible plant. Its stems are rich in polysaccharides and other bioactive compounds and are widely used for nourishing Yin， moistening the lungs， and enhancing immunity. Pectin methylesterases （PMEs） are key enzymes that catalyze the demethylesterification of pectin and are involved in plant cell wall modification， growth and development， and responses to environmental stresses. Their activity is finely regulated by pectin methylesterase inhibitors （PMEIs）. Therefore， investigating the characteristics and functions of the PME and PMEI gene families in D. officinale is important for improving its medicinal value and stress tolerance. Based on the chromosome-level genome of D. officinale and using two identification methods， a total of 46 DoPME genes （33 type I and 13 type II） and 31 DoPMEI genes were identified. Phylogenetic analysis showed that DoPMEs were classified into four clades （A-D）， while DoPMEIs were divided into three clades （A-C）. Domain， motif， and gene structure analyses indicated that genes within the same clade had relatively conserved structural features. Intra-and interspecific synteny analyses suggested that these two gene families followed an evolutionary pattern consistent with Orchidaceae， including early divergence， long-term independent evolution， and subsequent conservation in closely related species. qRT-PCR and expression analyses revealed distinct expression patterns of DoPMEs and DoPMEIs across different tissues and developmental stages， with relatively higher expression levels in roots， flowers， and perennial stems. This study provides a systematic analysis of the DoPME and DoPMEI gene families in D. officinale， offering a foundation for further functional studies and potential genetic resources for improving stress resistance and medicinal quality.