The speculative circuit is a kind of special parallelizing circuits which could execute the sequential operations in parallel by breaking the dependencies between them through the prediction approach. That is, the consumer operations no longer needs to wait the computed results of the corresponding product ones by predicting them, so that the consumer operations can be executed with the corresponding product ones at the same time. However, the predicted value is speculatively generated, so there still needs an additional recovery mechanism which will recover the speculative execution when the predicted value is detected not to match the computed one. Therefore, the dedicated conflict management mechanism and data synchronization mechanism are needed when designing a speculative circuit. In this paper, we present a new design model called “transactional speculative circuit model” (TSCM), which is based on the concept of transactional memory (TM), to design the speculative circuits. Moreover, this model also can be used to design non-speculative parallelizing circuits. We use TSCM to design a new speculative MPEG-2 encoder, and the experiment results show the performance can be efficiently improved.