Chǔfá yīngdāng yǔ fànzuì de yánzhòng chéngdù xiāng pǐpèi.
The punishment should match the severity of the crime.
Tips
grammar
程度 (degree/extent) turns adjectives into measurable nouns. 严重 + 程度 = 'seriousness as a measurable quantity', much like English adding '-ness' or 'level of'.
