The relationship between line tension and bending rigidity of extended bilayer membrane is studied in this paper.Extensive simulations of bilayer membrane with different projected areas were performed

and three regions have been found

i.e.

freely fluctuating membrane

extended membrane and extended membrane with a pore.Surface tension () calculated from stress tensor is in good agreement with that (fluc) calculated by fitting the membrane fluctuation data in freely fluctuating region and extended region except that at the transition point fluc is a little higher than .By introducing a very simple model

line tension of the pore can be calculated from bending rigidity and membrane thickness which is ignored in the classical Helfrich model

on the other hand

bending rigidity can be determined by line tension and membrane thickness.The results in the pore region show that the bending rigidity got from the simple model is in good agreement with the bending rigidity calculated by fitting the membrane fluctuation data in the freely fluctuating region and extended region.A convenient method for measuring the bending rigidity of bilayer membranes is then proposed.