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 \Lambda CDM 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 \pm 0.153 ( 68 \% C.L .
) , which implies that the flat DGP model is incompatible with the current observations , while the pure \Lambda CDM 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 .