Moderate rain and heavy rain elimination equations y₁, y₂ and discriminant equation y₃ of heavy rain are established with normalized sample rejection method T₄₂ model output in May-June,1990-1991. The y₁,y₂ equations decreases the forecast "Occurrence" while the weather is no occurrence,y₃ equation decreases the forecast "No"while the weather is occurrence. Conveyance using these three equations is more effective than using single one equation. "CSI"score increases obviously. Experimental forecast made in 1992 is better.