Abstract: In this paper,the polynomial of a complex variable s(≡x+iy) with real coefficients K=f(s)≡a₀sⁿ+a₁s^n-1+……+a_n-1s+a_n is graphically represented by three plane curves which are the projections of a space curve on three coordinate planes of the coordinate system(x,iy,K)in which K is confined to be real,The projection on(x,iy)plane is just the root locus of polynomial with K as a real parameter,It is remarkable that the equation of the root locus is mth degree of y²,whether。n=2m+1 or n=2m+2.In addition to the real curve K_r=f(x) in the figure(K,x),there exists another curve K_c which is plotted by the real parts of all complex roots against those of K.The(K,iy)curve is particularly important to determine the absolute as well as the relative stability interval of K for linear systems,For cybernetics,the(K,iy)curve can be used to show the relation between the natural frequency ω and the gain K.Such three figures are useful for studying the theory of equation and cybernetics.