Abstract: Although there was no legal source defense system in the legislation of new plant varieties, it had been widely used in the disputes of infringement of new plant varieties. The right of new plant varieties was also a kind of intellectual property rights. This system was the basic defense of intellectual property rights infringement. The system and civil law allowed analogous application, and the application of the defense of legal source in the infringement of new plant varieties was justified. To construct a complete defense system for the legal source of infringement of new plant varieties, it was necessary to learn useful experience from three aspects: existing relevant legislative provisions, judicial practice viewpoints, and foreign legislation. The requirements should include subjective ignorance and objective evidence to prove that there was a legal source. Whether it could be established or not should be based on whether it could be proved that there was evidence to prove the actual purchase, whether the propagating material had a seed business license, and whether the comprehensive consideration was too low. If the lawful source defense was established, no compensation was required, but the necessary expenses for rights protection must still be paid. If it was not established, punitive damages would only be applied under serious circumstances. Those who provided propagating materials to sellers were advised to participate in the litigation as a third party, and should perform the obligation to inform that they should be authorized for sale before providing propagating materials, but they did not perform the obligation to review whether they were actually authorized.