The Halbach magnet array has become more and more attractive in many electromagnetic engineering domains such as electrical motors for its potential features such as self-shielding and providing sinusoidal field distribution. This paper develops analytical models formulated in polar coordinates for predicting the field distribution of a segmented Halbach magnet cylinder with or without back iron. Based on the analytical models, the relationships between the air-gap flux density and four design parameters including pole-pair number, segment number per pole, permanent-magnet radial dimension, and air-gap length are analyzed. Further, the Taguchi method is employed to identify the settings of design parameters and determine the parameters which have a significant effect on the field distribution. The analytical models are verified by taking advantage of the finite-element method (FEM), which shows that all the results can be of considerable use in the design of permanent-magnet machines.