Subscript[P, 0]=10^5;Subscript[\[Rho], L]=998;Subscript[\[Eta], L]=0.001;Subscript[\[Sigma], L]=0.0725;c=1500.;\[Gamma]=1.4;Subscript[\[Rho], s]=7700;\[Nu]=0.27;r1=1.5*10^-6;r2=2.0*10^-6;H=1/100*r2;M=1.9*10^11;Subscript[p, a]=10^5;\[Omega]=2 2*10^4 \[Pi];f=2*10^4;T=2 Pi/\[Omega];
V1=142/105;V2=752/105;V3=1536/35;V4=88/35;V5=142/105;V6=1768/105;V7=4;V8=-4/3;V9=-2;V10=244/105;V11=4;V12=-(324/35);
nn1=NDSolve[{y1'[t]*(r1+x1[t])
+3
/2*y1[t]^2-1/Subscript[\[Rho], L]*((Subscript[P, 0]+(2*Subscript[\[Sigma], L])/r1)(r/(r1+x1[t]))^(3*\[Gamma])-(2*Subscript[\[Sigma], L])/(r1+x1[t])-(4*Subscript[\[Eta], L]*y1[t])/(r1+x1[t])-Subscript[P, 0]+Subscript[p, a]*Sin[\[Omega]*t])==1/4*y2[t]^2-(y3'[t]*(r2+x3[t])^2+2*(r2+x3[t])*y3[t]^2)/(x4[t]-x2[t])+((r2+x3[t])^2*(y2[t]*y3[t]+(r2+x3[t])*y4'[t]+5*y3[t]*y4[t]))/(2*(x4[t]-x2[t])^2)-((r2+x3[t])^3*y4[t]*(y2[t]+2*y4[t]))/(2*(x4[t]-x2[t])^3),y3'[t]*(r2+x3[t])+3/2*y3[t]^2==1/4*y4[t]^2-(y1'[t]*(r1+x1[t])^2+2*(r1+x1[t])*y1[t]^2)/(x4[t]-x2[t])-((r1+x1[t])^2*(y4[t]*y1[t]+(r1+x1[t])*y2'[t]+5*y1[t]*y2[t]))/(2*(x4[t]-x2[t])^2)-((r1+x1[t])^3*y2[t]*(y4[t]+2*y2[t]))/(2*(x4[t]-x2[t])^3)-H*(2*y3'[t]+2*y5'[t])-(Subscript[\[Rho], s]*H*y3[t]*(4*y3[t]+4*y5[t]))/(Subscript[\[Rho], L]*(r2+x3[t]))+(Subscript[\[Rho], s]*H*(2*y3[t]^2+2*y4[t]^2+y5[t]^2*V1+4*y3[t]*y5[t]+y6[t]^2*V2+2*y4[t]*y6[t]*V8))/(Subscript[\[Rho], L]*(r2+x3[t]))-(M*H*((8*(r2+x3[t])-2*x6[t]*V7+4*x6[t])-2*(1-\[Nu])*(4*(r2+x3[t])-x6[t]*V9-x6[t]*V11)))/(2*(1-\[Nu]^2)*Subscript[\[Rho], L]*(r2+x3[t])^2),((r1+x1[t])*y2'[t])/3+y1[t]*y2[t]+\!\(
\*SubscriptBox[\(\[PartialD]\), \(t\)]\((\((r1 + x1[t])\)*
\*SuperscriptBox[\((r2 + x3[t])\), \(2\)]*y3[t])\)\)/(x4[t]-x2[t])^2-((r2+x3[t])^2*((r1+x1[t])*(r2+x3[t])*y4'[t]+(r2+x3[t])*y1[t]*y4[t]+5*(r1+x1[t])*y3[t]*y4[t]))/(x4[t]-x2[t])^3==(-12*Pi*Subscript[\[Eta], L]*(r1+x1[t])*y2[t])/(2*Pi*Subscript[\[Rho], L]*(r1+x1[t])^2),((r2+x3[t])*y4'[t])/3+y3[t]*y4[t]-\!\(
\*SubscriptBox[\(\[PartialD]\), \(t\)]\((\((r2 + x3[t])\)*
\*SuperscriptBox[\((r1 + x1[t])\), \(2\)]*y1[t])\)\)/(x4[t]-x2[t])^2-((r1+x1[t])^2*((r1+x1[t])*(r2+x3[t])*y2'[t]+(r1+x1[t])*y3[t]*y2[t]+5*(r2+x3[t])*y1[t]*y2[t]))/(x4[t]-x2[t])^3+(2*H*Subscript[\[Rho], s]*y3[t]*(4*y4[t]+2*y6[t]*V8))/((r2+x3[t])*Subscript[\[Rho], L])+(H*Subscript[\[Rho], s]*(4*y4'[t]+2*y6'[t]*V2))/Subscript[\[Rho], L]==(-12*Pi*Subscript[\[Eta], L]*(r2+x3[t])*y4[t])/(2*Pi*Subscript[\[Rho], L]*(r2+x3[t])^2),((r2+x3[t])*y5'[t])/2+y3[t]*y5[t]==(-2*y3[t]^2)/V1-((r2+x3[t])*y3'[t])/V1-(M*((4*x5[t]*V1+2*x6[t]*V4-2*x6[t]*V5)-(1-\[Nu])*(2*x5[t]*V1+x6[t]*V10)))/(4*(r2+x3[t])*Subscript[\[Rho], s]*V1*(1-\[Nu]^2)),((r2+x3[t])*y6'[t])/2+y3[t]*y6[t]==-((y3[t]*y4[t]*V8)/V2)-((r2+x3[t])*y4'[t]*V8)/(2*V2)+(M*((2*x6[t]*V3-2*(r2+x3[t])*V7+2*x5[t]*V4+2*x6[t]*V6-4*(r2+x3[t])-2*x5[t]*V5)-2*(1-\[Nu])*(-(r2+x3[t])*V9+x5[t]*V10-(r2+x3[t])*V11+2*x6[t]*V12)))/(4*V2*Subscript[\[Rho], s]*(r2+x3[t])*(1-\[Nu]^2)),y1[t]==x1'[t],y2[t]==x2'[t],y3[t]==x3'[t],y4[t]==x4'[t],y5[t]==x5'[t],y6[t]==x6'[t],x1[0]==0,x2[0]==0,x3[0]==0,x4[0]==10 r1,x5[0]==0,x6[0]==0,
y1[0]==0,y2[0]==0,y3[0]==0,y4[0]==0,y5[0]==0,y6[0]==0},{x1,x2,x3,x4,x5,x6,y1,y2,y3,y4,y5,y6},{t,0,4000 T},MaxSteps->10^8]
上面是我的原代码，运行的时候报错总是无法求解以找到导数的明确公式，请各位大神帮我找找错误吧，我找了好几天都找不到

看了一眼，方程中出现的符号r无定义。你先改了试试