Monitoring of crustal deformation in real-time or near real-time means that the system must be capable to determine the possible variation in position within a minimum of time delay and guarantee alarm if specified limits are exceeded. With the GPS techniques, it is nowadays possible to install permanent deformation monitoring systems, which are working automatically. To cover the requirements of these systems, data flow and processing must be carried out online and the results have to be available in real-time, so that an overall deformation monitoring of the object is feasible. The GPS “Real Time Kinematic” (RTK) method, with fixing ambiguities “On The Fly”, stands for a very accurate and reliable technique that can fulfil the needs of the real-time accurate processing. In this paper, emphasis is taken on the algorithms that can be applied in the GPS permanent deformation monitoring system. A new algorithm for fixing the double difference phase ambiguities is introduced. The real-time and near real-time capability of this algorithm for monitoring the deformation of permanent stations, that are separated over lengths ranged between 30 to 120 km, is tested