data = {{43.68, 1.}, {206.42, 0.76}, {398.11, 0.58}, {1019.47,
0.42}, {1910.44, 0.33}, {2964.39, 0.26}, {4116.84,
0.22}, {5318.17, 0.19}, {6505.9, 0.16}, {7709.48, 0.15}, {8827.55,
0.13}, {9984.18, 0.12}, {11015.08, 0.11}};
model = Sum[
4/((2*k + 1)*Pi)*1(*c0*)*
MittagLefflerE[\[Beta], ((-d)*(2*k + 1)^2*\[Pi]^2*t^\[Beta])]*
Sin[(2*k + 1)*Pi*1/2], {k, 0, 10}];
M = NonlinearModelFit[data, model, {{\[Beta], 0.0029}, {d, 0.71}}, t];
General::ovfl: Overflow occurred in computation.
General::ovfl: Overflow occurred in computation.
General::ovfl: Overflow occurred in computation.
General::stop: Further output of General::ovfl will be suppressed during this calculation.
NonlinearModelFit::nrlnum: The function value {Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[],Overflow[]} is not a list of real numbers with dimensions {13} at {\[Beta],d} = {0.0467468,-0.359457}.
请问一下，最后的报错是什么原因啊

数太大了，已经不是提高精度能解决的了。是不是有约束没加？

可以试一下拟合的时候把 model 换成 model /. d -> d^2

LZ在stackexchange也问了：
mathematica.stackexchange.com/q/268159/1871
然后，虽然现在吧里没有强制规定，但是，如果你在别处也问了同样的问题，还望把相关链接附一下，免得有人做白工。