Abstract: The return signals from airborne laser depth sounding have dynamic ranges that exceed the capabilities of the sequential measurement equipments.The study on gain controlling of photomutiplier tubes(PMT) GDB-333,GDB-49 and R1333 have been carried out.The results show that the signal dynamic range can be compressed to 2.5×104orders by controlling the electric potential of grid and eletromutiplier electrode.The method of changing PMT gain to detect signals from sea bottom is very compatible to airborne laser depth sounding.