Dual-function radar-communication (DFRC) system plays a crucial role in various fields such as military, aviation, maritime, and wireless communication. This study proposes a method for designing integrated waveforms with orthogonal constant modulus under an integral sidelobe constraint for DFRC system. Efficient waveform design is crucial for achieving reliable and interference-resistant radar communication. We formulate an optimization algorithm with the objective function of maximizing signal-to-noise ratio (SNR). The integral sidelobe constraint is introduced to mitigate the impact of sidelobes on system performance and improve interference resilience. By controlling the integral sidelobe levels, the waveform design effectively reduces interference between multi-channels. The proposed waveform design method is evaluated through simulation experiments. The results demonstrate that the DFRC integrated waveform design with orthogonal constant modulus and integral sidelobe constraint significantly improves SNR and reduces communication error rate compared to traditional waveforms.