Why did Japan lose more soldiers in China I'm ww2?

Because Japan was in a war with china for like 5 or so years before ww2 officially started for the US. Thats what led them to attack us. We cut off the oil and trade to japan because of their Increasing aggression against all of the neighboring Asian countries. Especially China, the japanese did unspeakable war crimes against them that they don't acknowledge to this day.

In both cases, (Nazis in Russia, Japanese in China) they lost more because of tactics. The Chinese and Russians both had nearly unlimited manpower, and could commit enormous armies to the field across very wide spaces. Both china and Russia depended on attrition....basically bleeding the other side dry. Even at Nanking, considered a decisive Japanese victory, the Japanese lost 40,000 men. Even though the Chinese lost three times that number, it was nothing to them, but a serious blow to the Japanese. Their frustration over their losses is what lead to the annihilation of the civilian population, now known as the Rape of Nanking.

If the British or Americans would start taking anything like that number of casualties, they would simply withdraw. It was a whole different kind of fighting.

History is always written by the Victors

It depends what you mean by "more."

More than what?