How a grain ahead affecting a dolphin's transmitting performance is examined. A finite element approach was applied to numerically simulate the acoustic field around a dolphin with a small grain ahead of it. Acoustic intensity distribution, beam pattern, angle of strong beam and 3dB beam width are compared to investigate the differences caused by the small grain ahead of the dolphin. Although the grain size is small, its effects on the acoustic field and dolphin's transmitting performance are unignorable. Studies show that both sound source level and 3 dB beam width become smaller and the strong beam direction is turned. The results might be useful for better understanding how the dolphin's transmitting performance is affected by inhomogeneous medium such as an unwanted small grain here.