In this paper, the problem of transmit beampattern design in multiple-input multiple-output (MIMO) radar with one-bit digital-to-analog converts (DACs) is investigated. The one-bit waveform sequence can be properly designed by minimizing the integrated sidelobe to mainlobe ratio (ISMR) of the transmit beampattern. However, due to the minimum ISMR criterion and discrete constraint, the formulated optimization problem for such a design is nonconvex and thus difficult to tackle directly. To this end, we employ the semidefinite relaxation (SDR) technique to modify the original problem to its convex counterpart. More importantly, the dimension of resulting large-scale semidefinite programming (SDP) problem is greatly reduced via exploiting the special block-spare structure. Simulation results will demonstrate the effectiveness and improved performance of our method.