u = 0.33;
Er = 1/(12.3*10^-12*(1 - u^2));
v = Sqrt[Er/7500];
a = 0.015;
l = 0.005;
e = 15.1;
w = k*v;
x = k*a;
Y = (I*w*e*Pi*a^2)/
l*(1 - 0.58^2 +
0.58^2*((1 + u)*BesselJ[1, x])/(
x*BesselJ[0, x] - (1 - u)*BesselJ[1, x]));
Z = 1/Y;
f = x/(2*Pi*a)*Sqrt[1/((1 - u^2)*7500*12.3*10^-12)]
NSolve[{x*BesselJ[0, x] == (1 - u)*BesselJ[1, x]}, k]
Plot[Norm@(Z), {k, 0, 700}]
555.1031891081523`*137.82424095932583`
555.1031891081523`*359.6737230889798`
555.1031891081523`*571.693401597557`

想要用x为横坐标，询问一下有没有什么办法

……你代换一下，或者用ParametricPlot就行了啊。