Abstract: Through observing and counting the quantity of algae cells,the article discussed effect on the growth rate of the algae from different nitrogen and phosphorus sources using Platymonus subcordiformis as the experimental object ,sodium nitrate, urea or ammonium sulphate as nitrogen source, potassium dihydrogen phosphate or sodium dihydrogen phosphate as phosphorus source. The results showed that in the culture solution of sodium nitrate, urea, ammonium sulfate, potassium dihydrogen phosphate and sodium dihydrogen phosphate , platymonas subcordiformis could grow normally, especially grow significantly in the urea and sodium dihydrogen phosphate solution. Urea (0.0512) was the most effectively than sodium nitrate (0.0325）and ammonium sulphate(0.0306) on the growth rate of the algae.In the orthogonal experiment, using disodium hydrogen phosphate and urea as the nitrogen and phosphorus source could significantly promote the algae growth, and at the end of index growth period, the algae cell concentration could reach up to 6.1×105 cell/mL, which was the most ideal bait concentration of flat algae used as live foods.