Modeling of air-gap flux density distribution produced by magnet poles is essential for analysis and design of linear permanent-magnet synchronous motors. This is usually done by time-consuming numerical methods which are difficult to be incorporated in iterative motor design procedures or by approximate models which lack desirable accuracy. This paper presents an alternative method to model the air-gap flux density distribution which is both accurate and simple enough to be integrated into iterative motor design procedures. It consists of the solution of an improved magnetic equivalent circuit and an air-gap flux density distribution function (FDDF). The end teeth effects and magnetic saturation of iron core can be taken into account in the modeling. Different motor characteristics are calculated by means of the proposed FDDF. The accuracy of the proposed method in modeling of the machines is verified by the finite-element method and its superiority over a recent method based on an extensive machine model is demonstrated