It mainly consists of an L-band normal-conducting high gradient single-cell rf gun with detachable cathode and a unique imaging system to precisely locate emitters on surface with a resolution of 20 um. Depending on cathode shape, a cathode electric field up to 700 MV/m is achievable for emission study. Various cathode properties, such as emission current, current density, uniformity, quantum efficiency, emittance, lifetime, could be characterized with well-developed diagnostics. The ACT beamline is also designed to be user-friendly with short cathode switching period and flexible running schedule.