Pathogen infection is a serious threat to plant growth and development, causing severe crop yield reduction. The plant immune system, which is mainly composed of PTI (pattern-triggered immunity) and ETI (effector-triggered immunity), plays an essential role in resistance against pathogen infection. A large amount of research focused on resolving the key immune receptors/co-receptors, the components and regulation mechanisms of the PTI and ETI signaling pathways, and the biosynthesis and signaling pathways of the plant immune hormones salicylic acid and jasmonic acid. The major events during plant immune responses include pathogen recognition, the outburst of reactive oxygen species, Ca²⁺ influx, MAPK cascade signaling, and the induced expression of downstream defense genes. Recent studies have revealed that the expression of plant immune-related genes is not only regulated at the transcriptional level. The stability, translation efficiency, and translation products of their mRNAs are affected by a variety of post-transcriptional regulatory mechanisms, including alternative splicing, m⁶A modification, small RNAs, uORFs, and R-motifs. Here, we summarized the present understanding of the plant immune system and mainly introduced the latest studies of the post-transcriptional regulation of plant immunity. This review also covered some findings that showed how pathogen interferes with the host post-transcriptional regulatory machinery. Some post-transcriptional regulatory elements have been successfully applied in crops. This application provides new molecular tools for improving diseases resistance and contribution to food security, as well as useful components for molecular breeding.