This paper models the complexity consumption of entropy decoding in a H.264 decoder, which includes many modes such as fix-length code (FLC), variable-length code (ExpGolomb code in particular), content-adaptive variable length code (CAVLC) and content-adaptive binary arithmetic code (CABAC). By analyzing the computations involved in different entropy decoding modes, we derive a complexity model that relates the total complexity with the total bit rate and slice mode (I or P or B). The model is shown to be very accurate when compared with the measured complexity in a PC running the H.264 decoder.