Abstract: After fuzzy-ball workover fluid was utilized in workover of Well C22 of SZ36-1 Oilfield, fluids production was decreased, oil production was increased and the watercut was reduced. How to evaluate reservoir damage by fuzzy-ball workover fluid has become a focal point. From fluid production, oil production and watercut trend 10 months before and after workover of Well C22, it was found that evaluating the effect of fuzzy-ball workover fluid for offshore SZ36-1 Oilfield using oil production tendency method is more suitable than average fluid production method. Oil production tendency method can analyze the rangeability of fluid production and oil production and rate of change before and after workover in detail, having a guiding significance for predicting oil production and formulating reasonable working system. Analyzing Well F20 with the oil production tendency method, another well in this oilfield worked over with fuzzy-ball fluid, better interpreted the fluid and oil production after workover, and could evaluate the extent of damage to the reservoir by fuzzy-ball workover fluid.