let's not believe him不要相信他,不是don't believe 而上面为什么不用加助动词“do"了?

let's not believe him不要相信他,不是don't believe 而上面为什么不用加助动词“do"了?
let's not believe him
不要相信他,不是don't believe 而上面为什么不用加助动词“do"了?

let's not believe him不要相信他,不是don't believe 而上面为什么不用加助动词“do"了?
let=do

祈使句啊