Formal:
* 天下太平 (tiānxià tàipíng): This literally translates to "peace under heaven" and is a very common and formal way to express peace on Earth.
* 世界和平 (shìjiè hépíng): This is the most direct translation of "world peace" and is also quite formal.
Informal:
* 地球和平 (dìqiú hépíng): This is a more casual and literal translation of "earth peace".
* 世界安宁 (shìjiè ānníng): This translates to "world tranquility" and conveys a sense of peacefulness and calmness.
Poetic:
* 人间净土 (rénjiān jìngtǔ): This translates to "pure land on earth" and is a more poetic way to express the ideal of peace.
The best way to say "peace on earth" in Chinese will depend on the context and your intended tone.