Pinus koraiensis and Fraxinus mandshurica as the dominant tree species in mixed coniferous-broad-leaved forest under three thinning intensities (low 15%, moderate 30%, and severe 50%) were studied in this paper. The competitive characteristics of Pinus koraiensis and Fraxinus mandshurica under different thinning intensities were quantified with three times repeated investigation and tree ring width data. The effects of varied competitive environment on radial growth were analyzed. The results showed that:1) the proportion of individual trees with change in competitive environment of Pinus koraiensis residual trees decreased with the increase of thinning intensity, but the proportion of retained trees with weakening competition was positively correlated with the thinning intensity. The largest proportion of Pinus koraiensis residual trees with weakening competition was 63%, in the heavy thinning plot. The proportion of individual trees with changed in competitive environment of Fraxinus mandshurica residual trees was the same in three plots, accounting for 50%. 2) In different competitive environments, the consistent radial growth trends of Fraxinus mandshurica,but differential radial growth trends of Pinus koraiensis were observed. The radial growth tendency of Pinus koraiensis reserved trees with weakening competition in low and heavy thinning plot was raised. The radial growth of Pinus koraiensis reserved trees with weakening competition in the moderate thinning plot, Pinus koraiensis reserved trees with unchanged competition in all plots and Fraxinus mandshurica reserved trees in different competition intensities were reduced in 2013 and 2014 (within 2012 after thinning), but promoted in 2015 (the third year after thinning). 3) With the increase of thinning intensity, the annual increment of radial growth of Pinus koraiensis reserved trees with weakening competition has been increased since 2015 (the third year after thinning), which was significantly higher than that of Pinus koraiensis reserved trees with unchanged competition (P < 0.05). Since from 2014 (the second year after thinning), the annual increment of radial growth of Fraxinus mandshurica reserved trees with weakening competition was increased, with the largest one in the heavily thinning plot, followed by the light thinning plot. The lowest increase in annual increment of radial growth was found in moderate thinning plot.