A channel estimation apparatus and method are provided to ensure that a channel estimation value can correctly reflect a transmission channel status, so that an orthogonal frequency division multiplexing (OFDM)-based wireless system can correctly transmit an aggregate long frame according to the channel estimation value. The channel estimation apparatus determines a first channel estimation value, receives a first symbol group of a long frame according to the first channel estimation value, and determines a second channel estimation value according to the first symbol group, and if a difference between the first channel estimation value and the second channel estimation value is less than or equal to a first threshold, determines a third channel estimation value according to the first channel estimation value and the second channel estimation value.