The invention provides a privacy protection method and system in mobile crowd sensing. The method comprises sensing data uploading, sensing data aggregation and sensing data transaction stages, and the system comprises a mixed excitation sensing module, a sensing data noise adding module, a user key generation module, a sensing data encryption module, an encrypted data uploading module, a sensingdata aggregation module, a sensing data decryption module, a secure multi-party computation module and a sensing data transaction auction module. By adoption of the privacy protection method and system, an effective mechanism is established to improve the degree of participation of the sensing user and the authenticity of the sensing data; and moreover, the leakage of the personal privacy data ofthe sensing user is effectively protected, the false data of malicious users is prevented, the computational overhead of the involved algorithm is low, a secure and efficient design target is achieved, the privacy protection method and system is suitable for large-scale promotion and use and can be applied to actual production and life processes.