In view of miniaturization of multi band transmission antenna in wireless communication system, this paper presents a miniaturized slot antenna, which is fed by L-shaped microstrip line, a slot with an opening at one end formed by three steps on the ground plane to cut off the current path, so as to realize dual-band coverage of WLAN band. The electromagnetic simulation software is used to simulate and optimize the parameters of the antenna, by changing the length and width of the slot, the antenna can work at 2.45GHz and 5.8GHz at the same time, the results show that the antenna port return loss S11≤-10dB, and the working bandwidth are 2.4~2.49GHz and 5.48~6.1GHz respectively, which meet the requirements of IEEE802 11b/g and IEEE802 11a/n standards. Meanwhile, the antenna is fabricated, and the port return loss, gain and radiation pattern are tested, the simulation results are in good agreement with the test results. Compared with the traditional planar slot antenna, the antenna proposed in this paper is compact in size, simple in structure, easy to implement and well to integrate with the circuit, which hopes a wide range of communication applications in the future.