The area of an equilateral triangle is $400\sqrt{3}{\text{ m}}^2$. Its perimeter is:

The area of an equilateral triangle with side length $a$ is given by the formula:
$$\text{Area}=\frac{\sqrt{3}}{4}{a}^2$$

Given that the area is $400\sqrt{3}{\text{ m}}^2$:

$$\frac{\sqrt{3}}{4}{a}^2=400\sqrt{3}$$

Canceling $\sqrt{3}$ from both sides:

$$\frac{a^2}{4}=400$$

$$a^2=1600$$

$$a=\sqrt{1600}=40\text{ m}$$

The perimeter of an equilateral triangle is given by:

$$\text{Perimeter}=3a=3\times 40=120\text{ m}$$