The invention discloses a frame synchronization method and a system of an OFDM system receiver. The frame synchronization method comprises the following steps: adopting a mask mode to select a mask cross-correlation sequence for a local synchronization cross-correlation sequence of the OFDM system receiver; Sampling a received signal of the OFDM system receiver, performing cross-correlation operation on the sampled data and the mask cross-correlation sequence, and determining whether the received data includes a preamble of a data frame according to the operation result; If the received data includes a preamble of a data frame, peforming cross-correlation operation between the input sample data and the local synchronous cross-correlation sequence of the OFDM system receiver, and determining the start position of the data frame of the received data according to the operation result. The frame synchronization method and the frame synchronization system of the OFDM system receiver can greatly reduce hardware resources without affecting the synchronization detection effect.