A method and device for using satellite trajectory extension data in a mobile apparatus. The device in accordance with the present invention comprises an I/O interface and a microprocessor. The input/output (I/O) interface is used for obtaining at least one satellite navigation message for a satellite. The microprocessor is used for determining a propagating condition according to the satellite navigation message, estimating a plurality of parameters of a satellite trajectory prediction model according to the propagating condition to establish an estimated satellite trajectory predication model, propagating a set of satellite trajectory extension data by using the estimated satellite trajectory prediction model, computing acquisition assistance data according to the satellite trajectory extension data and acquiring signals of the satellite by using the acquisition assistance data.