  We propose a new approach to the consistency test of dark energy models with
observations. To test a category of dark energy models, we suggest introducing
a characteristic Q(z) that in general varies with the redshift z but in those
models plays the role of a (constant) distinct parameter. Then, by
reconstructing dQ(z)/dz from observational data and comparing it with zero we
can assess the consistency between data and the models under consideration. For
a category of models that passes the test, we can further constrain the
distinct parameter of those models by reconstructing Q(z) from data. For
demonstration, in this paper we concentrate on quintessence. In particular we
examine the exponential potential and the power-law potential via a widely used
parametrization of the dark energy equation of state, w(z) = w_0 + w_a z/(1+z),
for data analysis. This method of the consistency test is particularly
efficient because for all models we invoke the constraint of only a single
parameter space that by choice can be easily accessed. The general principle of
our approach is not limited to dark energy. It may also be applied to the
testing of various cosmological models and even the models in other fields
beyond the scope of cosmology.
