Fast algorithms of code acquisition and tracking for DS/SS are presented based on software radio. Code acquisition can be done via calculating the cycle-correlation between received IF signal and local matched filter, using the auto-correlation's sharp characteristic of PN sequence. Two fast algorithms for cycle-correlation are presented. Their correct acquisition probabilities and average acquisition times are analyzed. Finally a simple algorithm of code tracking and its precision are presented. The correctness and validity of these algorithms have been tested by simulation and experiment, and they can be used especially when the SNR is very low and the size and power of the instruments are strictly limited.