An angle-measuring method includes: configuring a state observer to calculate a set of estimated signals based on a set of previously calculated estimated parameters; configuring the state observer to calculate a gain thereof using a dynamic equation associated with a gyroscope; configuring the state observer to calculate a set of currently calculated estimated parameters using the dynamic equation associated with the gyroscope based on the gain calculated by the state observer, a set of sensing signals generated by a sensing module, and the estimated signals calculated by the state observer; and configuring an angle calculator to calculate an angle of rotation of the gyroscope based on a position and a velocity in the currently calculated estimated parameters calculated by the state observer and a stiffness coefficient of the gyroscope. An angle-measuring gyroscope system that implements the angle-measuring method is also disclosed.