The invention discloses a preparation method of a praseodymium doped potassium-sodium niobate film and an application thereof, relates to a preparation method of a potassium-sodium niobate film and an application thereof, aims to solve the problem that an existing optical stress sensing technology is based on change of shapes of monitored samples and is poor in sensitivity, and provides a new method for monitoring stress by using luminescence characteristics of praseodymium ions. The method comprises the following steps: step one, preparation of a praseodymium doped potassium-sodium niobate target; and step two, preparation of a praseodymium doped potassium-sodium niobate film by a gas phase method. High-sensitivity sensing of stress is implemented by monitoring material luminescence characteristics caused by the stress, and the problem that the existing optical stress sensing technology is low in sensitivity is solved. A film deposition method provided by the invention is easy to operate, preparation of the praseodymium doped potassium-sodium niobate film on different types of substrates can be implemented, and large-scale production is facilitated. The preparation method is used for preparing the praseodymium doped potassium-sodium niobate film.