In order to improve the performance of the space-time block codes in multiple input and multiple output communication system, this paper proposes a new kind of quasi-orthogonal space-time block codes (QOSTBC) combined with the constellation rotation. Through the constellation rotation quasi-orthogonal space-time block codes (CR-QOSTBC), a certain decoding of simplicity can sacrifice themselves to avoid the bit rate decreased when the number of orthogonal space-time block codes (OSTBC) is greater than 2 to encode with LDPC code. The multiple input and multiple output communication system can be used to solve the problem of the multipath effect, and obtain high diversity gain. The simulation results show that this new kind of coding method can effectively reduce the bit error rate, and can also improve the performance of the system compared with the QOSTBC system without the constellation rotation. When the bit error rate is 10-5, the CR-QOSTBC combined LDPC can improve by 1.8 dB compared with the QOSTBC combined LDPC. When the bit error rate is 10-3, the CR-QOSTBC combined LDPC can improve by 5.3 dB compared with the QOSTBC.