Abstract: With comparing balance output for profits and losses between hand labour and a loader at the Timber Yard of Weiguo Forestry Bureau, Yunnan Province, their mathematical models for maximum annual output were established, and sloved by a computer. Finally, with comparing production cost between hand lahour and the loader, the critical output completed by the loader is 26610m³, safe operation rate 95.9%. Meanwhile, the critical output for various amount of loaders is also defined.

Key words: Timber yard, Balance output for profits and losses, Critical output