  It is well established that the nucleon form factors can be related to
Generalized Parton Distributions (GPDs) through sum-rules. On the other hand,
GPDs can be expressed in terms of Parton Distribution Functions (PDFs)
according to Diehl's model. In this work, we use this model to calculate
polarized GPDs for quarks ($\widetilde{H}_q$) using the available polarized
PDFs obtained from the experimental data, and then study the axial form factor
of nucleon. We determine parameters of the model using standard $\chi^2$
analysis of experimental data. It is shown that some parameters should be
readjusted, as compared to some previously reported values, to obtain better
consistency between the theoretical predictions and experimental data.
Moreover, we study in details the uncertainty of nucleon axial form factor due
to various sources.
