  The accelerating expansion of our universe at present could be driven by an
unknown energy component (Dark Energy) or a modification of general relativity
(Modified Gravity). In this note we revisit the constraints on a
phenomenological model which interpolates between the pure \LambdaCDM model and
the Dvali-Gabadadze-Porrati (DGP) braneworld model with an additional parameter
\alpha. Combining the cosmic microwave background (CMB), baryon acoustic
oscillations (BAO) and type Ia supernovae (SNIa), as well as some high-redshift
observations, such as the gamma-ray bursts (GRB) and the measurements of linear
growth factors (LGF), we obtain the tight constraint on the parameter
\alpha=0.254\pm0.153 (68% C.L.), which implies that the flat DGP model is
incompatible with the current observations, while the pure \LambdaCDM model
still fits the data very well. Finally, we simulate the future measurements
with higher precisions and find that the constraint on \alpha can be improved
by a factor two, when compared to the present constraints.
