Due to the multi-peak of Binary Offset Carrier(BOC) autocorrelation function, an unambiguous acquisition algorithm of BOC signal based on time-domain filter is designed. The frequency response of the time-domain filter is obtained, then the filter coefficients are deduced to construct a Finite Impulse Response(FIR) filter. The simulation of different algorithms shows that the time domain filter can completely eliminate the side peaks of BOC autocorrelation. The filter order is reduced and an achievable unambiguous acquisition algorithm of BOC signal based on time- domain filter and Multi-bank Matched Filter(MMF)-Fourier Transform(FFT) is designed. The simulation analysis shows that the algorithm can eliminate side peaks and capture the signal correctly.