In order to improve the transmission performance in inter-symbol interference channel, a controlled inter-symbol overlapping transmission scheme to obtain high frequency efficiency, which is called inter-symbol overlapping transmission (ISOT), is studied. ISOT allows $K$ symbols to be simultaneously transmitted without increasing channel bandwidth, and the symbol transmission interval can be decreased to $Ts/K$, assuming that $Ts$ is the symbol duration. In additive white gaussian noise(AWGN) channel, we study the ISOT system which symbol rate is greater than system bandwidth. Though inter-symbol overlapping transmission doesn't increase channel bandwidth, the spectrum efficiency can be increased by $K$ times in theory. Simulation results show that ISOT can achieve higher spectrum efficiency compared with high dimension modulation, even if low dimension BPSK or QPSK modulation is used. Furthermore, we integrate ISOT with single-carrier frequency domain equalization(SC-FDE) and evaluate its BER performance. Simulation results show that ISOT integrated with SC-FDE has significant performance improvement comparing to SC-FDE with ^{K}$-QAM, while ISOT uses QPSK modulation to transmit $K$ symbols simultaneously. Simulation also shows that the more the symbols overlapping, the more the performance improvement. Inter-symbol overlapping transmission scheme can be used in mobile device and used as a uplink transmission technology in mobile communication systems, such as B3G or 4G, to provide higher spectrum efficiency.