To support very high data rate services that require higher system capacity, the High Speed Downlink Packet Access (HSDPA) was proposed in the UMTS standard. One of key techniques supporting the HSDPA services is the Adaptive Modulation and Coding (AMC) in which the modulation scheme and the coding rate are adaptively changed to match the current channel condition reported by the user equipment (UE). Therefore, the mapping relationship between the Channel Quality Indicator (CQI) and Signal to Interference Ratio (SIR) is closely related to the accuracy of AMC and the performance of HSDPA. This paper proposes a SIR to CQI mapping method that satisfies the 3GPP requirements. In order to verify the performance of the proposed mapping method, we implemented the link-level simulator which is composed of all the physical layer blocks depicted in the 3GPP standard. With the proposed mapping method, we show that UE can report the exact channel condition and the system can yield performance exceeding the requirements in the 3GPP technical specification.