PN code capture is a difficult problem in radio reconnaissance and navigation warfare. The PN code capture under self-jamming code was studied from the point view of pattern recognition theory. The carrier frequency and phase of self-jamming code were estimated and compensated firstly. Thus the PN code capture was converted into pattern recognition problem. Combined with the periodicity of the short PN code, binary integration was introduced to reduce the SNR before decision, which made the direct demodulation of spread spectrum signals feasible without large diameter antenna.