Atom Trap Trace Analysis(ATTA) technology, which is based on the theory of laser cooling and trapping, has the capability of high-sensitivity detection of the radioactive isotope of Krypton and wide applications in the fields of geophysics and environmental science. Zeeman slower, as a key component of the ATTA instrument, is used to generate continuous atomic beam with low velocity. With the advantages of stable magnetic distribution, easy installment and debugging, no constant current power or cooling requirement, the Zeeman slower based on permanent magnet is getting more and more attention in recent years. In this paper, a Zeeman slower based on the toroidal permanent magnet was designed, the spatial distribution of the magnetic field of this slower was calculated by finite element analysis, a prototype was manufactured according to the design parameters, and its magnetic field along the axis was also measured. The lengths of the slower and its effective deceleration area were 51.2 cm and 46.9 cm, separately. The maximum deviation between the measured and theoretical magnetic field was less than 3.6 G, and the average deviation was 1.3 G. Furthermore, the deceleration process of the atomic beam in the designed and actual magnetic field distribution was simulated, and the influence of the radial variation of magnetic field distribution on the deceleration process of the atomic beam was analyzed. The result shows that the Zeeman slower in this paper is able to decelerate the velocity of the atomic beam with a diameter less than 20 mm from the maximum initial value of 250 m/s to the final value of 50 m/s.