Both W-CDMA and cdma2000 are strong candidates for third generation mobile communications systems. Based on the physical layer standard of cdma2000, the performance analysis of fixed-point simulations is presented in this paper on cdma2000 1x downlink. The effects of quantization and finite wordlength, which have typically been assumed negligible in floating-point simulations, become significant for fixed-point simulations. The complete fixed-point simulation platform for cdma2000 1x downlink is developed by EDA tool - COSSAP. The structure and performance of the key component in cdma2000 systems, the RAKE receiver, are discussed in details. Comparisons of results between floating-point and fixed-point simulations lead to some important conclusions, which provide certain references for the implementation of practical systems.