Quantum secure direct communication (QSDC) is an important branch of quantum cryptography.It can transmit secret information directly without establishing a key first,unlike quantum key distribution which requires this precursory event.Here we propose a QSDC scheme by applying the frequency coding technique to the two-step QSDC protocol,which enables the two-step QSDC protocol to work in a noisy environment.We have numerically simulated the performance of the protocol in a noisy channel,and the results show that the scheme is indeed robust against channel noise and loss.We also give an estimate of the channel noise upper bound.