This paper proposes an analytical no-load magnetic field model taking account of the curvature coefficient to compute the noload magnetic field of parallel direct-driven conjoined permanent magnet synchronous motor (PDC-PMSM). The shortcomings of the 3-D finite element method are avoided, such as the time-consuming and sensitive to finite element meshes. As well as, putting forward the design method of the motor. A 2-D subdomain model of PDC-PMSM can be obtained by segment 3-D model at the average radius, which is quasi to linear permanent magnet synchronous motor. Based on Maxwell's equations, the Poisson's equations in the permanent magnet (PM) subdomain and the Laplace's equations in the subdomain between air gap and PM are calculated under no-load condition. The radial and tangential flux density of each subdomain are obtained by the Fourier's series, hyperbolic functions, separation of variables, and the boundary condition. Better yet, the curvature coefficient is introduced to reduce the error between the analytical magnetic field in the planar model and the tubular model. The analytical no-load magnetic field model is established more accurately. The expression of curvature coefficient and back-electromotive force are derived. One prototype is manufactured for simulation and experimental study. The accuracy and feasibility of the proposed model are verified by the prototype test.