Tackling interference is an essential issue for the wireless system, which benefits the quality of service (QoS). In this paper, we consider an integrated sensing and communication (ISAC) system and focus on suppressing the signal-dependent interferences (SDIs) toward the radar and exploiting the constructive part of multi-user interference (MUIs) in communication. A novel optimization problem to minimize the transmitting power considering the channel fluctuations is formulated. We propose a tailored semidefinite relax (SDR) and successive convex approximation (SCA) based algorithm to simultaneously design the beampattern and symbol-level waveform. Simulations show that the proposed algorithm outperforms the conventional robust design method and a heuristic algorithm based on waveform scaling, reducing power consumption.