The end-to-end distance distribution of a grafted compact polymer chain confined between two parallels is studied by using the PERM （pruned-enriched-Rosenbluth method）algorithm.Because of the difference in different directions of confined polymer chains

in this paper we just consider the distribution function P(x) in the x-axis direction

and it can be expressed as ln［P(x)/Pm(x)］/ND-2/3=a0+a1u+a2u2+a3u3

here u=x/ND-2/3

N is the chain length

Pm(x) is the maximum value of P(x)

D+1 is the distance between the two parallels.On the other hand

we calculate the Shannon entropy according to P(x)

which is very sensitive to the variation of the distance of two parallels

and it can be used to describe the restriction of the polymer chain.With a given chain length N

the Shannon entropy of the distribution P(x) decreases rapidly first and then tends to a fixed value with increasing D

by which we can find a transition point Dc.When DDc the Shannon entropy tends to a constant

and at the same time the restriction of polymer chain performed by the two parallels can be ignored.We also find that the relationship between Dc and N as Dc-Nλ

here λ=0.543.