The invention belongs to the technical field of satellite navigation, and discloses an inter-symbol difference and code parallel GPS weak signal capturing method and system. Comprising a digital down-conversion module, a code merging module, a data storage module, a Doppler stripping module, a data folding module, a step-by-step matching coherence module, an inter-symbol difference module, a Doppler compensation module, a step-by-step coherence module, a step-by-step incoherence module, a peak value judgment module, a Purler search completion judgment module, a Doppler regulation and control module and a result output module. According to the high-orbit GPS signal capturing method based on inter-symbol difference and code parallelism, a rapid and efficient capturing algorithm is provided for a navigation receiver; an inter-symbol difference algorithm is adopted to avoid the influence of navigation data jump on the coherent integration duration, and the capture sensitivity of the GPS signal is improved by improving the coherent integration duration. According to the invention, a step-by-step coherent algorithm and a step-by-step incoherent algorithm are adopted, so that rapid acquisition of signals with different intensities is realized, and the first positioning time of a navigation receiver is shortened.