A sample of intra-day variable sources was observed with the 25m radio telescope of Xinjiang Astronomical Observatory (Liu X. et al. 2012, Marchili et al. 2010). In study of this subject, we developed a stand-alone software package to analyze the observing data from epoch to epoch. We found that the strong and rapid variability are mainly induced by inter-stellar scintillation (ISS). ISS induced variability can be proved by the observed annual modulation in source variability time-scales. So far annual modulation effect was detected in ~10 sources, in which 4 sources were detected in Urumqi.

In the meantime, we studied the influence of core size change on the variability strength and time-scale. Our results indicated that there is a delay between increasing of VLBI core fluxes and the intrinsic source size. The increasing of intrinsic source size can weaken or even quench the ISS induced variability (Liu X. et al. 2012).

IDV observations were also performed for the study of the first three-month Fermi bright AGN list. We found that IDV detection rate in Fermi AGNs is significantly higher than in the other FSRQ samples. The result imply that the core of Fermi AGN is more compact thus easier to cause either ISS or intrinsic variability (Liu X. et al. 2011). In addition, we found inter-planet scintillation (IPS) effect in IDVs for the first time (Marchili et al. 2011).

Moreover, we surprisingly found that the flux density of M82 – one of our calibrators, showed a steep increasing and later on a slow decreasing in 2008. Analysis revealed that the variability was a superimposition of a supernova explosion on a long-term variability (Marchili et al. 2010). The follow-up VLBA observation of this source presented the subsequent evolutionary scene.

Recently we initialed a northern sky IDV survey. The paper on this project is in preparation (Liu J. et.al).