It would help to know which conference. From the information you gave, I can narrow it to the Quebec Conference or the Cairo Conference, and I suspect the Cairo Conference is the one in question, or at the very least I can state why Stalin was not there. Stalin did not attend the Cairo Conference because Chiang Kai-shek was there. China was at war with only Japan and the Soviet Union had a non-aggression pact with Japan, so Stalin refused to attend a war conference at which China was represented so as to avoid alarming the Japanese.
Thanks. Cairo Conference