It is shown that the transport of the plasma immersed in a stochastic magnetic field (s.m.f.) must lead to the producing of an ambipolar electric field. In this paper, the transition probability of charged particels in the s.m.f. was derived in the case of existing a transverse electric field. The transport fluxes and the ambipolar electric field were then calculated. The result shows that the ambipolar electric field is insensitive to the collision between particles. ((|e|E)/Te=-A1/ne(dne)/(dx), A is a coefficient ofabout 1, which depends on collision insensitively.) This ambipolar electric field may be used as a necessary (but not sufficient) criterion of ascertaining whether the effect of s.m.f. on the plasma transport is important. In the transport process induced by s.m.f. the impure ions transport more rapidly than hydrogen ions (VI/Vi≈[mi/mI]1/2ZI>1), this result can be used to explain the phenomenon in Tokamak experiment, i.e., when there appears interior disruption, the impurities will be extracted from centre region instead of being cumulated. We discussed also the effect of collision and the condition under which the above treat-ment is applicable. In the case of high collision, the diffusion flux is a much smaller quantity. The corresponding dynamic equation of plasma in a s.m.f. has been derived, it is somewhat different from that obtained by K. Molvig et al. in [3].