UHF-INDO LCAO SCF MO oaloulations of oyanoacetio acid free radical (NCCHCOOH) were carried out.The program used is Pople's CNINDO.Data caloulated for radical structure of cyanoacetic acid are presented and oompared with available experimental results in Tables 1 and 2 and Fig.2-7 in the Chinese Text.It is confirmed by ESR spectra study and INDO calculation that the free radical trapped in the irradiated single crys七al of cyanoacetic acid is in the form of NCCHCOOH.Molecular orbital coefficient,electron density,net atomic charge,spin density and hyperfine coupling constant are calculated for NCCHCOOH radical.