The threshold signcryption is a very useful cryptographic primitive. Recently, a generalized group-oriented threshold signcryption scheme was proposed by Peng et al.(PENG C, LI X, LUO W. A generalized group-oriented threshold signcryption schemes [J]. Acta Electronica Sinica, 2007, 35(1): 64-67), but Wang (WANG Y. Cryptanalysis and improvement of threshold signcryption scheme [J]. Computer Engineering and Applications, 2012, 48(1): 125-127) pointed out that there was a weakness in it because of the management of the keys, and an improved scheme was given. But both of the two schemes have the similar encryption structure, that is, if some members of the signcryption group colluded together in the key generation stage, they could avoid the authentication and deny that they had taken part in process of the signcryption. Furthermore, an improved group-oriented threshold signcryption scheme was proposed to resist the above attack and the attack proposed by Wang. It not only inherits the advantages of the above schemes, but also is more efficient in the process of parameters exchange.