To classify the role of ferredoxin NADP⁺ oxidoreductase (FNR) in the process of soft rot resistance in Oncidium, we cloned a OnFNR gene (Genbank accession No. KX461907) from ‘Little Cherry’ Oncidium by using RACEPCR. Bioinformatics analysis and subcellular localization analysis of OnFNR were performed, and qRTPCR was used to analyze the expression pattern of OnFNR in different organs and different soft rot infection stages. Moreover, the overexpression vector of OnFNR was constructed and transformed into protocormlike bodies (PLBs) to investigate its function in Oncidium soft rot resistance. The results showed that: (1) the OnFNR gene contains an open reading frame of 1 080 bp that encodes 359 amino acids. The predicted molecular mass is 40 066.14 Da, and the isoelectric point is 8.72. OnFNR contains two typical domains: FAD binding domain and NADP⁺ binding domain, and it is subcellularly located in the chloroplast. (2) Multiple sequence alignment and phylogenetic tree analysis revealed that OnFNR is clustered with other plant LFNRs, and is close to Phalaenopsis equestris LFNR (89.1%). (3) qRTPCR results showed that the expression level of OnFNR was significantly higher in the leaf than that in flower and pseudobulb, and the lowest expression was found in root. Moreover, after the plants were inoculated with the soft rot pathogen, the expression of OnFNR was significant downregulated in pseudobulb and leaf at only 1 day post pathogen inoculation (dpi) (P<0.01), and the expression levels of the five susceptible stages were all lower than that of the healthy plants. (4) The overexpression vector pCAMBIA1301OnFNR was successfully constructed, and it was successfully transformed into Oncidium PLBs by agrobacterium EHA105 infection, and 16 transgenic PLBs overexpressing OnFNR were obtained. In the overexpressed OnFNR PLBs of Oncidium, both OnFNR and Fd gene expression were significantly upregulated, especially the expression of Fd was increased to 3.67 times of the control (nontransgenic PLBs). Moreover, the survival rate of PLBs overexpressing OnFNR was 48.88% on the 4th day of soft rot pathogen infection, while the control was only 6.66%. This study shown that: OnFNR is a photosynthetic ferridoxin NADP+ oxidoreductase located in chloroplast, and overexpression of OnFNR can significantly improve the disease resistance of plants. It is speculated that OnFNR plays an important role in plant resistance to virus and ROS outbreak, and overexpression of OnFNR may promote signal transduction of MAPK pathway by improving electron transfer efficiency of LET and increasing Fd expression.