The invention discloses a medical safety tracing method and system based on a block chain. The method includes the following steps: S1, medical data is saved to a main node of a block chain; S2, medical institutions collect medical data during medical treatment; S3, experts and doctors make medical plans according to the medical data and sign the medical plans, and the record is saved to the blockchain and broadcasted; S4, the state of illness is judged; if the illness is mild, a patient gets medicines and then goes to the nurse station for transfusion to complete treatment; or, surgical treatment is arranged, preoperative physical examination is carried out, the result is saved to the block chain, and the method goes to S5; S5, surgical treatment is carried out, and the signature data during operation is saved to the block chain; S6, after treatment is completed, the medication and vital signs of the patient are recorded regularly, saved to the block chain and updated in real time; and S7, after the patient is discharged from the hospital, the daily medication of the patient is recorded in real time and saved to the block chain. The method and the system have the advantage that:through the information anonymity and decentralization of the block chain technology, medical institutions can obtain medical data through private keys under the permission of patients to achieve information sharing.