The detection of angular positioning error on specific turntable shaft end cannot reflect its actual space angular position of working surface. Thus, a space angular position measuring device of turntable working surface is introduced with circular grating and horizontal capacitance sensor as its angle measuring components. The error factors of the measuring device are especially classified and analyzed in order to improve spatial angle measurement accuracy. Besides the angle measuring error of subsystem, the measuring device has error that the shafting or the sensitive direction of horizontal capacitance sensor is not parallel to the reference plane for measurement and others error terms. The mathematical model is established to analyze the factors of systematic errors and correct them according to the spatial geometrical relations of grating rotary surface, sensitive direction of sensor, rotation axis and reference plane for measurement. Then the measuring device is calibrated by using highprecision turntable with 0.3″ indexing error. And the mathematical model of error compensation is established based on radial basis function (RBF) neural network to improve precision with the maximum error value decreased to 2.9 ″ from 13.75 ″ to satisfy angular measuring accuracy within 3 ″ demand.