The mixture of water sample, catalyst dissolution wave, and strong oxidant dissolution solution is heated to 115 ℃. Polyphosphate and other phosphorus containing compounds in the water sample are dissolved and oxidized by strong oxidants under acidic conditions of high temperature and high pressure to generate phosphate ions. In the presence of a catalyst, phosphate ions form a colored complex in a strong acid solution containing molybdate. The analyzer detects the color change and converts it into total phosphorus value output. The amount of colored complex generated is equivalent to the total phosphorus content.