The utility model provides an array antenna of a roadside unit and an electronic toll collection (ETC) system. The array antenna mainly comprises an antenna matrix, and a feed network connected with the antenna matrix, wherein the antenna matrix is a 1*6 antenna matrix, 6 antenna elements are horizontally and symmetrically distributed around a column center line of the antenna matrix, two sides of a center line of the antenna matrix are respectively provided with 3 antenna elements, and the feed network comprises a feeding point, output ports and microstrip lines. According to the array antenna of the roadside unit, the impedance matching method is adopted to reduce the complexity of the feed network, the array antenna has the advantages of stable performance, simple structure, low cost and good low minor lobe level, the horizontal half-power angle of 20 degrees is in full accord with the current market requirements of ETC roadside units, and the problem of adjacent lane interference in the ETC system can be effectively solved.