The invention relates to an orthogonal sine and cosine axial angle encoder signal detecting and converting circuit, comprising a singlechip module, an interval discriminating circuit and an encoder. The circuit can convert an orthogonal sine and cosine wave axial angle signal value output by the encoder into a pulse train signal used for calculating rotating speed and a position of a motor. The singlechip module discriminates a signal output by the circuit according to signal amplitude and an interval of the encoder, an angle value is calculated, if the calculated angle value is positioned at the first half part of a period of a square wave pulse signal, a high level is output, otherwise, a low level is output when the calculated angle value is arranged at a second half part of the period of the square wave pulse signal, and thus an orthogonal pulse train corresponding to a sine and cosine signal is formed. An angle is calculated by adopting a straight line linear function approximation method within the margin of an error. The circuit disclosed by the invention is applicable to feedback and acquisition of running speed and position information of the motor of a servo system and has the characteristics of few occupied computer resource, low hardware cost, fast detection and conversion speed and high accuracy.