我假设您的id类型为string

在这种情况下，您需要将其转换为适当的Mongo ObjectID

If this is the case, you need to convert it to a proper Mongo ObjectID

尝试此代码:

var ObjectID = require('mongodb').ObjectID;

function findUser(id, cb) {
    MongoClient.connect(cs, function(err, db) {
        var col = db.collection('users');
        col.findOne({ _id: new ObjectID(id) }, function(err, user) {
            return cb(err, user);
        });
    });
}