For the ATSC-Mobile DTV standard has much more training-sequence than the conventional ATSC digital television standard, in this paper, we propose a modified channel estimation structure using the additional training sequence to track the channel changes, which can fast start-up the receiver equalizer of ATSC-M/H digital television system in time varying mobile broadcasting channel. A dual threshold scheme is also proposed to switch the CMA and DD algorithm smoothly, it is not like conventional DMCMA algorithm with no error rebound caused by the algorithm change, the scheme is based on the equalizer's output SER.