  We present a model-independent method of reconstructing scale factor against
lookback time from the Observational Hubble parameter Data (OHD). The
reconstruction method is independent of dynamical models and is only based on
the Friedmann-Robertson-Walker metric. We also calculate the propagation of
error in the reconstruction process. The reconstruction data errors mainly come
from trapezoidal rule approximation and the uncertainty from OHD. Furthermore,
the model discrimination ability of original OHD and reconstructed a-t data is
discussed under a dimensionless standard method. a-t data can present the
differences between cosmology models more clearly than H-z data by comparing
their coefficients of variations. Finally, we add fifty simulated H(z) data to
estimate the influence of future observation. More Hubble measurements in the
future will help constrain cosmological parameters more accurately.
