The conformations of DNA chains are studied under the elastic rod model by Metropolis Monte Carlo simulation．The energy of DNA chains includes the bending energy EB and the twisting energy ET

and they can be expressed in the form of EB (r)=A—2∫L0κ2 ds and ET(r)=2π2C—L(ΔLk-Wr)2．The energy decreases with increasing the chain length of DNA．We find that EB is greater than ET by 10～102 times．In the same time

the relationship between 〈Rg2〉 and chain length n is 〈Rg2〉=1169.5-3.5×n+0.025×n2．The equation of Lk=Wr+Tw is verified

and the values of Lk and Wr are found to be very close to each other．It shows that DNA chain is easier to be bent than to be twisted．But for the large value of Lk

the tendency of torsion becomes large．Oursimulation can provide a new method to analyze the conformations of DNA chains．