A training method for a memory system is provided. The memory system includes a memory controller and a memory. The memory controller is connected with the memory. The training method includes the following steps. Firstly, the memory samples n command/address signals according to a first signal edge and a second signal edge of a clock signal to acquire a first sampled content and a second sampled content. The memory selectively outputting one of the first sampled content and the second sampled content through m data signals to the memory controller in response to a control signal. Moreover, m is larger than n and smaller than 2n.