We propose a deterministic quantum secure direct communication protocol by using dense coding.Thetwo check photon sequences are used to check the securities of the channels between the message sender and the receiver.The continuous variable operations instead of the usual discrete unitary operations are performed on the travel photonsso that the security of the present protocol can be enhanced.Therefore some specific attacks such as denial-of-serviceattack,intercept-measure-resend attack and invisible photon attack can be prevented in ideal quantum channel.Inaddition,the scheme is still secure in noise channel.Furthurmore,this protocol has the advantage of high capacity andcan be realized in the experiment. We propose a deterministic quantum secure direct communication protocol by using dense coding. The paper check photon sequences are used to check the securities of the channels between the message sender and the receiver. Continuous variable operations instead of the usual discrete unitary operations are performed on the. travel photonsso that the security of the present protocol can be enhanced. Herefore some specific attacks such as denial-of-serviceattack, intercept-measure-resend attack and invisible photon attack can be prevented in ideal quantum channel.Inaddition, the scheme is still secure in noise channel.Furthurmore, this protocol has the advantage of high capacity andcan be realized in the experiment.