The relationship between the inter-annual variations of the earth rotation, atmospheric angular momentum (AAM), sunspot number and El Ni o is analyzed. The result shows that the inter-annual variation of the earth rotation responds to the variation of AAM and the pregnancy of El Ni o timely. Generally, the inter-annual component of the earth rotation will reach zero in a changing process that increases from the negative to the positive extreme before El Ni o occurs about half year or more. And the solar activity may have certain influence on the appearance of El Ni o. We consider that El Ni o will possibly appear around the end of 2001.