Communication delay， mass data processing and sampling data lost or error caused by electromagnetic disturbance during transmission are the problems which must be faced in digital protection. Two data processing scheduling schemes: sampling data driving method and timing scheduling with preset data buffer， are analyzed. Data processing methods separately based on equal interval sampling and fixed point sampling per cycle are designed. The action strategies of digital protection in case of invalid sampling data are proposed. The proposed schemes have been applied to a digital protection device， which has passed the test of real time digital simulator（RTDS） and dynamic analog experiment of electric power systems.