The elastic behavior of protein-like chains was investigated by using the Pruned-Enriched-Rosenbluth Method (PERM). Three typical protein-like chains such as all-α

all-α

and α +β(α/β)proteins were studied in our modified orientation dependent monomer-monomer interaction (ODI) model. We calculated the ratio of R2/N and shape factor δ* of protein-like chains in the process of elongation. In the meantime

we discussed the average energy per bond U/N

average contact energy per bond Uc/N

average helical energy per bond Uh/N and average sheet energy per bond Ub/N. Three maps of contact formation

-helix formation

β-sheet formation were depicted. All the results educe a view that the helix structure is the most stable structure

while the other two structures are easy to be destroyed. Besides

the average Helmholtz free energy per bond A/Nis was presented. The force f obtained from the free energy was also discussed. It was shown that the chain extended itself spontaneously first. The force was studied in the process of elongation. Lastly

the energy contribution to elastic force fu was calculated too. It was noted that fu for all-β chains increased first

and then decreased with x0 increasing.