Zhōngguó shì shìjiè shàng gāngtiě chǎnliàng zuì dà de guójiā.
China is the country with the highest steel production in the world.
Tips
usage
The 量 (quantity) suffix is very productive for measurements: 产量 (output), 数量 (quantity), 质量 (quality - note: quality, not quantity!), 重量 (weight), 容量 (capacity).
grammar
产量 is typically modified with 高/低 (high/low), not 大/小 or 多/少: 产量很高 (output is high), 产量低 (output is low).