Abstract: A new method for solid-liquid separation in micro-fluidic system is proposed on the basis of digital micro-fluid technology.The motion of solid particles in the micro-fluidic channel of micron scale is controlled from the outside of the micro-fluidic system by means of inertial force field produced from the piezoelectric ceramic actuators.Solid-liquid separation is realized due to the velocity difference between micro-fluid and solid particles in the micro-fluidic channel.The separation and selection of solid particles with different density is brought to effect as a result of velocity difference between solid particles in the micro-fluidic channels.It is proved that inertial force still plays a leading role in solid-liquid separation of micron scale.As solid particles usually stick to the surface of the micro-fluidic channels, which leads to difficulty in solid-liquid separation, it is essential to eliminate or weaken the influence of surface force with the aid of surface hydrophobization to the micro-fluidic channels.This method is adopted to drive and separate all kinds of solid particles such as inorganic particles, organic particles and particles with biological activity in the micro-fluidic system, and is especially fit to separate solid particles from high concentration suspension in the micro-fluidic channels which are difficult to separate in other ways.