"由他独力地" 可以翻译为 "entirely on his own" 或 "single-handedly by him" 。其中，“entirely on his own” 更侧重于表达完全依靠自己、不依赖他人的意思，在日常和书面语境中都较为常用；“single-handedly by him” 强调独自一人完成，语气稍强，可根据具体语境和表达需要选用。
例句：
He completed the difficult project entirely on his own.（他独自完成了这个困难的项目。）
He managed to solve the problem single-handedly by him.（他独自一人设法解决了这个问题 。 ）