Within the mean-field model,the coherent matter waves of a dipolar condensate in a harmonic potential superimposed to a deep lattice are investigated by the variational principle.It is shown that,in a harmonic potential superimposed to a deep lattice,it is possible to control the decoherence of Bloch oscillations due to the fact that the on-site and the inter-site dipolar interactions can not only damp out Bloch oscillations but also maintain long-lived Bloch oscillations under the certain condition.In particular,long-lived Bloch oscillations of dipolar condensate can be realized when the dipolar interaction,the contact interaction,the frequency of the harmonic potential and initial width of the wave packet satisfy an analytical condition.Thus the decoherence of Bloch oscillation can be controlled by adjusting the dipolar interaction,the contact interaction,the frequency of harmonic potential and the initial width of the wave packet. Within the mean-field model, the coherent matter waves of a dipolar condensate in a harmonic potential superimposed to a deep lattice are investigated by the variational principle. It is shown that, in a harmonic potential superimposed to a deep lattice, it is possible to control the decoherence of Bloch oscillations due to the fact that the on-site and the inter-site dipolar interactions can not only damp out Bloch oscillations but also maintain long-lived Bloch oscillations under the certain condition.In particular, long-lived Bloch oscillations of dipolar condensate can be realized when the dipolar interaction, the contact interaction, the frequency of the harmonic potential and initial width of the wave include satisfy an analysis condition. Here the decoherence of Bloch oscillation can be controlled by adjusting the dipolar interaction, the contact interaction, the frequency of harmonic potential and the initial width of the wave packet.