Genetic analysis of the dwarf rice mutant CHA-2 by space mutation was studied.The results indicated that its dwarf trait was controlled by two recessive semi-dwarf genes without linkage,sd1 and a new nonallelic to sd1 gene named as iga-1.The new semidwarf plant H2 with the new iga-1 gene from a cross between Huiyangzhenzhuzao and CHA-2 was insensitive to exogenous gibberellin,so it was speculated that the H2 semi-dwarf mutant was the gibberellin insensitive dwarf mutant.