  Using the maximum-entropy method, we calculate the end-to-end distance
distribution of the force stretched chain from the moments of the distribution,
which can be obtained from the extension-force curves recorded in
single-molecule experiments. If one knows force expansion of the extension
through the $(n-1)$th power of force, it is enough information to calculate the
$n$ moments of the distribution. We examine the method with three force
stretching chain models, Gaussian chain, free-joined chain and excluded-volume
chain on two-dimension lattice. The method reconstructs all distributions
precisely. We also apply the method to force stretching complex chain
molecules: the hairpin and secondary structure conformations. We find that the
distributions of homogeneous chains of two conformations are very different:
there are two independent peaks in hairpin distribution; while only one peak is
observed in the distribution of secondary structure conformations. Our
discussion also shows that the end-to-end distance distribution may discover
more critical physical information than the simpler extension-force curves can
give.
