ex_modify_instance_attribute and create_node has AuthFailure error use AWS EC2 driver

When I use AWS EC2 driver invoke create_node and ex_modify_instance_attribute API , I got this error:
raise InvalidCredsError(err_list[-1])
libcloud.common.types.InvalidCredsError: 'AuthFailure: AWS was not able to validate the provided access credentials'

But ex_create_subnet/ list_nodes API success , and I'm sure about I have the permission on AWS IAM to create EC2 instance.

By the way , I am using AWC cn-north-1 region.