The effect of [S] on strength and toughness of low alloy steel plates in which sum of [P], [N], T[O] is less than 8x10 5 and the effect of T[O] on strength and toughness of the steel plates in which sum of [S], [P], [N] is less than 7x10~5 were investigated. It is found that the strength of the steel plates decreases with increasing [S] content when [S] is less than 4x10~5. When [S] varies within the range of 4×10~(-5)-1.2×10~(-4), [S] has no significant effect on strength of the steel. The strength of the steel plates increases with increasing T[O] content when T[O] is less than 30×10~(-6), but decreases with increasing T[O] when T[O] is more than 3×10~(-5). The difference between the LETT in plate length direction and LETT in width direction decreases with decreasing [S] content. However, even when [S] is decreased to 9×10~(-6), the difference of the LETT is still 16℃. When T[O] varies between 1.8×10~(-5) and 5.2×10~(-5), the low temperature impact toughness of the steel plates slowly decrease The effect of [S] on strength and toughness of low alloy steel plates in which sum of [P], [N], T [O] is less than 8 × 10 5 and the effect of T [O] on strength and toughness of the It is found that the strength of the steel plates decreases with increasing [S] content when [S] is less than than 4x10 ~ 5. When [S] varies within the range of 4 × 10 -5 -1.2 × 10 -4, [S] has no significant effect on strength of the steel. The strength of the steel plates increases with increasing T [O] content when T [O] is less than 30 × 10 -6, but decreases with increasing T [O] when T [O] is more than 3 × 10 -5. The difference between the LETT in plate length direction and LETT in width direction decreases decreases with decreasing [S] content. However, even when [S] is decreased to 9 × 10 -6, the difference of the LETT is still 16 ° C. When T [O] varies between 1.8 × 10 -5 and 5.2 × 10 -5, the low temperature impact toughness of the steel plat tes slowly decrease