  GAIA leads us to step into a new era with a high astrometry precision of 10
uas. Under such a precision, astrometry will play important roles in detecting
and characterizing exoplanets. Specially, we can identify planet pairs in mean
motion resonances(MMRs) via astrometry, which constrains the formation and
evolution of planetary systems. In accordance with observations, we consider
two Jupiters or two super-Earths systems in 1:2, 2:3 and 3:4 MMRs. Our
simulations show the false alarm probabilities(FAPs) of a third planet are
extremely small while the real two planets can be good fitted with
signal-to-noise ratio(SNR)> 3. The probability of reconstructing a resonant
system is related with the eccentricities and resonance intensity. Generally,
when SNR >= 10, if eccentricities of both planets are larger than 0.01 and the
resonance is quite strong, the probabilities to reconstruct the planet pair in
MMRs >= 80%. Jupiter pairs in MMRs are reconstructed more easily than
super-Earth pairs with similar SNR when we consider the dynamical stability.
FAPs are also calculated when we detect planet pairs in or near MMRs. FAPs for
1:2 MMR are largest, i.e., FAPs > 15% when SNR <= 10. Extrapolating from the
Kepler planet pairs near MMRs and assuming SNR to be 3, we will discover and
reconstruct a few tens of Jupiter pairs and hundreds of super-Earth pairs in
2:3 and 1:2 MMRs within 30 pc. We also compare the differences between even and
uneven data cadence and find that planets are better measured with more uniform
phase coverage.
