Generalized spatial modulation （GSM） technology transmits information by selecting part of the transmitting antenna. This system has a low transmission rate due to some antennas remaining silent. To improve the transmission rate of the system， all the transmitting antennas of the GSM are activated. The system still can hardly recover the transmitted signal at the receiving end. In this paper， a two-mode generalized spatial modulation system is proposed， the information bits sent in each time slot of the system are divided into index bits and constellation modulation bits， and all transmitting antennas are divided into two groups by the index bit. Two distinguishable constellation modulation symbols are transmitted simultaneously on two groups of antennas. The maximum likelihood （ML） algorithm is used to detect and demodulate the transmission symbol at the receiver. The proposed system achieves the balance between transmission efficiency and system performance. Analysis and simulation show that when the bit error rate is 10^-3， the dual-mode generalized spatial modulation system is compared with the GSM and the multiple input multiple output （MIMO） system with same total transmit power and transmission rate. The former adopts low-order modulation to maximize the Euclidean distance between constellation points， which can obtain a gain of about 4 dB， while the latter can improve the performance of detection algorithm through power index at the receiver end， which can obtain a gain of about 2 dB.