This paper presents a mobile coverage measurement system for ATSC DTV networks. This system adopts four omni-directional antennas and one directional antenna on the roof of the vehicle. These antennas are connected with DTV channel and RF analyzers independently for the space diversity. All the analyzers are connected to the control computer by Ethernet and the measurement data is collected synchronously. With this mobile measurement system, it becomes more efficient to find coverage gaps inside DTV networks and suitable places for the installation of small power on-channel repeaters to fill those coverage gaps.