a = {7, 7, 7};
b = {-2, -1, -3}; S1 =
Table[NDSolveValue[{Derivative[1][z][t] == m[t],
Derivative[1][m][t] == (-1)/(z[t]^3), z[0] == a[[i]],
m[0] == b[[i]]}, {z, m}, {t, 0, 2}], {i, 1, Length@a}];
ParametricPlot[
Table[{S1[[i, 1]][t], S1[[i, 2]][t]}, {i, 1, Length@a}], {t, 0, 4}]
用mathematics画出来的相图与实际不符，上面是程序，求大神指教