Wuzhen is at its best in spring (March to May) and autumn (September to November), when the weather is mild and the light on the canals is soft. Summers are hot and humid but manageable; the water town atmosphere means there is shade and there are breezes off the canals. Winter is cool but quiet — the Chinese tourist crowds thin considerably, and the town has a more authentic feel.
Chinese national holidays (particularly Golden Week in late September/early October and the Spring Festival in January/February) bring enormous domestic crowds to all the water towns. If possible, visit on weekdays. The Wuzhen Theatre Festival in late October brings international theatre companies to stages set up throughout the town, and is worth timing a visit around if you have any interest in contemporary performance.