The dynamic properties of charge-density waves in orthorhombic TaS3 are studied as a function of the electric field at several temperatures. In the sliding state, we found that the field dependence of non-linear current carried by CDW changes abruptly at a certain electric field V-c. Moreover, the power of fundamental component in narrow-band noise has a minimum value at the same electric field. These results imply the existence of a dynamic transition between plastic-flow and moving-solid. (C) 2000 Elsevier Science B.V. All rights reserved.