Zhè chǎng kàngyì yùndòng jùyǒu hěn qiáng de zìfāxìng.
This protest movement had a strong spontaneous character.
Tips
grammar
自发性 is a noun formed with the suffix 性 (-xìng), which converts words into abstract quality nouns: 自发 (spontaneous) → 自发性 (spontaneity). Common pattern: 可能性,必要性,重要性。