The present invention provides a frame synchronizer of T-DMB system receiver and its method, the device includes adder 1, selftimer 1, adder 2, selftimer 2. adder 3, a comparator, a sign counter and a decision control state machine, wherein the adders 1, 2, the selftimers 1, 2 are used for receiving input signal and the sending in the adder 3 after dot difference; the adder 3 sends the processing result to the comparator and then sends to the sign counter, the sign counter sends the enumerated data to the decision control state machine and receives the feedback of the decision control state machine. The frame synchronizer processes counting by receiving the signl of the signal width and the difference of threshold, and judging null interval, the method is quick and high effect, only using some control state machines and simple adding unit can realize because of having no filter, the method reduces the spending of the hardware, effectively overcomes time pulse.