The invention discloses a privacy protection electronic voting method and system based on a block chain, and the method comprises the steps: determining a voting rule, and building a plurality of voting nodes and one or more verification nodes in the block chain according to the voting rule; generating a voting key and a corresponding homomorphic encryption algorithm according to a preset rule; each node of the plurality of voting nodes receiving votes from voting participants, encrypting the votes according to the voting key, and sending the encrypted votes to a verification node; the verification node receiving the encrypted votes sent by the plurality of voting nodes, and performing voting statistical calculation according to the homomorphic encryption algorithm to obtain an encrypted voting statistical result; decrypting the encrypted voting statistical result according to a decryption key corresponding to the voting key to obtain a voting statistical result. According to the method and the system, public transparency and privacy security assurance of electronic voting are realized by setting a key and based on homomorphic encryption and zero knowledge proof.