Comparisons of transient voltage stability characteristics between induction generators and induction motors are conducted. In correspondence with that of the induction motors， transient voltage stability criterions and stability margin definition for induction generators are proposed. The impacts on transient voltage stability of both node voltage and rotor speed are comprehensively considered. A multi-criteria assessment process is designed to speed up the evaluation for the cases far away from the critical condition， and to ensure the accuracy for the cases close to the critical condition. Sensitivity analysis is performed based on the fault critical clearing time obtained through trial-and-error based on full scale time domain simulations. The results prove the accuracy of using the proposed criterion and margin index to reflect the degree of induction generators voltage stability.