In modern dialects, some words of "voice relaxation for variation" came from ancient times or did do not occur in modern times, such as "只_只管" and "指_指头." However, it is difficult to find documentary evidence or no documentary evidence is available in common books of words or books of rhymes, and the history of their formation is unknown. We can approach this phenomenon by combining time and place, associating reality with history, connecting language factors with social factors, in combination with other materials, to infer the historical age of its formation and its causes. The author explores the original characters of some dialect words with outstanding characteristics, and believes that some words in northern dialects should have been recorded by borrowing words long ago. The exploration of the original Chinese characters can also find clues from the ancient "voice relaxation for variation." The voice relaxation for variation of "只_只管" and "指_指头" could be traced back to the Wei and Jin Dynasties. The original word of "擦" in the Shanxi dialect words "水不擦" and "不擦子" is "池."