Timing synchronization is an important component in a receiver designed to recover data form sampling digital waveform. A synchronous sampling recovery with dual correlator differential (DCD) based acquisition with effects of auto-gain controller (AGC) is proposed to achieve fast timing acquisition for direct sequence / code division multiple access (DS/CDMA) system over frequency-selective fading channel in this paper. It measures both received DCD difference power to determine the good sampling phase from an all-digital phase interpolator based multiphase generator. This solution can tolerate + 50ppm system clock offset (SCO) under frequency-selective fading channel. Hence, we not only to determine the good sampling phase fast, but also to arrive stable variable gain amplifier (VGA) with AGC controller in DS/CDMA system approaches.