The infrared signature has been used extensively to discriminate exoatmosphere objects. The performance of the discriminating system is heavily dependent on the choice of features. Although numerous features have been extracted, the shape and micromotion parameters still serve as important additional features. However, there is little research on extracting the shape and micromotion parameters from the infrared signature. An estimating method of the nutation angle and half cone angle for a precession conical object is investigated. The time variation of an IR signature is found to be complicated yet valuable for estimating the micromotion and shape parameters. Based on the fact that the temperature changes a small amount during a short interval, the band exitance of the object in a short time window is approximated to be a constant to reduce the number of the model parameters. A least square estimator is used to estimate the nutation angle and half cone angle from the IR signature. Simulation experiments and the resulting discussion are carried out to demonstrate the effectiveness of the proposed estimation method.