  We present multi-frequency observational results for the Compact
Steep-Spectrum (CSS) quasar 3C309.1. The observations were carried out with the
VSOP at 1.6 and 4.8GHz and the VLBA at 15.4GHz. The source has a distorted,
one-sided radio jet. Relativistics effects and physical properties are
discussed. Comparing the predicted and observed X-ray fluxes in the framework
of the synchrotron self-Compton model we derive the beaming factor for 3C309.1.
The complex structure of the jet may be explained by a relativistic helical
flow in a heterogeneous, clumpy ISM.
