The open-sleeve antenna is analyzed using the method of moment. Emphasis is given to the analysis of the VSWR (Voltage Standing Wave Ratio) of the antenna. The multi-band characteristic of the sleeve antenna are investigated. The 1st and the 3rd frequency bands come from the driven dipole and the 2nd frequency band is due to the length of parasitic elements and the distance between the driven element and the parasitic elements. Some useful results are presented and discussed in this paper.