Timber properties of autotetraploid Paulownia tomentosa are heritable with whole genome duplication, but the molecular mechanisms for the predominant characteristics remain unclear. To illuminate the genetic basis, high-throughput sequencing technology was used to identify the related unigenes. 2677 unigenes were found to be significantly differentially expressed in autotetraploid P. tomentosa. In total, 30 photosynthesis-related, 21 transcription factor-related, and 22 lignin-related differentially expressed unigenes were detected, and the roles of the peroxidase in lignin biosynthesis, MYB DNA-binding proteins, and WRKY proteins associated with the regulation of relevant hormones are extensively discussed. The results provide transcriptome data that may bring a new perspective to explain the polyploidy mechanism in the long growth cycle of plants and offer some help to the future Paulownia breeding.