Taking into consideration of acquisition time, algorithm performance and hardware implementation these three aspects, this paper developed a nondecision-aided maximum- likelihood code acquisition algorithm suited for low SNR environment. The acquisition time is small because it can detect all possible code phases in one treatment. We also analyzed a signal decision scheme based on elementary hypothesis-testing theory, and lead to an adaptive threshold detection plan which is easily to implement in hardware. In the end, this scheme's performance is theoretically evaluated by analyzing its detection probability and false detection probability.