A regular expression matching method and system, and a searching device are provided. First, the searching device performs string filtering on a data stream to be matched, in which if keywords in the data stream and preset character words have at least one same character, the searching device indicates that the data stream passes through the string filtering. Then the searching device performs regular expression filtering on the data stream passing through the string filtering. In a string filtering process through the method, system, and device, when Hash mapping positions of the keywords of the data stream are a subset of the Hash mapping positions of the character words, it indicates that the data stream passes through the string filtering, and it is not required to store the keywords and further compare the keywords with the character words, thereby saving the storage space and improving performance.