Non-contact labyrinth clearance seal was presented to replace the packing seal of the piston of down-hole-pump.Two-dimensional groove model of labyrinth-clearance seal was set up,and the effect of groove width and groove depth on the leakage was analyzed by adopting SST turbulent model and SIMPLE algorithm and based on ANSYS Fluent simulation software.The arrangement of the groove with limited length was explored.The results indicate that there is a positive correlation between the leakage and the groove width when the seal depth is fixed.The leakage is the smallest when the width depth ratio is about 2∶1 while the groove width is more than 1mm,and the trend of flattening of the leakage is occurred while the width-depth ratio reach to 1∶1.The leakage of seal is first increased and then decreased in a certain seal length along with the increasing of the distance between grooves or the decreasing of the distance among grooves and the inlet and outlet of clearance.So the rational matching of the distance among grooves and the inlet and outlet of clearance is important to get good sealing property.