Abstract: A direct blind recovery method based on SemiDefinite Relaxation (SDR) technique is proposed to detect Short Burst Data (SBD) signals in cooperative relay networks. Without channel state information and signal statistics information, SBD sequences can be recovered directly by the proposed method. Firstly, the mathematical model of blind SBD signal detection in cooperative communication systems with one relay is presented. Then, the cost function of least square estimation for high order Quadrature Amplitude Modulation (QAM) signals is formulated. Meantime, SDR technique is introduced to solve the optimization problem, which leads to a low-rank approximate solution toward the optimal one efficiently. Finally, simulation results verify that the proposed method owns good performance and fast convergence rate. Furthermore, all the results imply that the proposed method provides a reference to those cases of SBD signal detection.