Spoofing is a huge threat to navigation system. Anti-spoofing in acquisition can firstly find spoofing signal. In this paper, a new method is proposed to alarm receiver whether there is a spoofing signal: in acquisition stage, if receiver finds two correlation peaks above a threshold for two times continuously, it indicates a spoofing signal; while if one peak, only if the rough signal-to-noise ratio is lower than a power threshold and the width of correlation function is lower than a width threshold, it has no spoofing signal. The theoretical calculation methods of thresholds above are all presented there. Also, the influence factors and performance analysis is presented. Results show that we give a quantitative power threshold; and by introducing the width of correlation function, it can deal with the condition that the authentic and spoofing signals are overlap, while methods existed can't. Our work is significant for designing anti-spoofing receiver.