放空炮

fire empty cannons;talk big;spout hot air;indulge in idle boasting;pay lip service
不要～，拿出行动来。Now,none of your empty talk. Let’s see how you act./我当时放了空炮，对形势作了过分乐观的分析。I then made some groundless (or pointless)remarks,assessing the situation over-optimistically./我们只能放放空炮。We can only voice some verbal support.