An in-depth analysis is made of the possible hidden risks to the traditional access system for electric power mobile operation based on the personal digital assistant（PDA）. A safer access system for electric power mobile operation based on PDA is then designed and implemented， with its architecture and components thoroughly analyzed. Capable of such functions as certificate verification of both the PDA and the safe access system， data transmission security， safe access control， network separating and data filtering， real-time monitoring and audit， etc， this system can effectively promote the security and protection of electric power mobile operation.