Effect of precipitation and solid-solution on slab's quality and product's mechanical properties is very important. Based on studying effect of carbon content, nitride content, niobium content and temperature on solid-solution of carbonitride, the following laws were obtained. Firstly, solid-solution temperature will rise when content of carbon, nitride and niobium increases. Secondly, effective activity of NbN goes upwards with increases of content of nitride, and amount of solid-solution of niobium reduces. Quantity of NbN rises with increase of content of niobium from 800°C to 1100°C. The same laws can also be used for effect of carbon content. Niobium ratio between solid-solution amount and total content rises with increase of temperature, the ratio value lies from 30% to 70%.