\!\(
\*SubsuperscriptBox[\(\[Pi]\), \(r\), \(N\)] = \(
\*SuperscriptBox[\(U\), \(N\)]\
\*SubsuperscriptBox[\(q\), \(r\), \(N\)] =
\*SuperscriptBox[\(U\), \(N\)]\ \((\[Alpha] + \[Delta]\
\*SubsuperscriptBox[\(P\), \(m\), \(N\)] - \((
\*SuperscriptBox[\(W\), \(N\)] +
\*SuperscriptBox[\(U\), \(N\)])\) -
\*SubscriptBox[\(\[Phi]l\), \(r\)] +
\*SubscriptBox[\(\[Phi]\[Sigma]l\), \(m\)])\)\)\)
\!\(
\*SubsuperscriptBox[\(\[Pi]\), \(m\), \(N\)] = \(
\*SubsuperscriptBox[\(P\), \(m\), \(N\)]\ \((\[Alpha] -
\*SubsuperscriptBox[\(P\), \(m\), \(N\)] + \[Sigma]\ \((
\*SuperscriptBox[\(W\), \(N\)] +
\*SuperscriptBox[\(U\), \(N\)])\) -
\*SubscriptBox[\(\[Phi]l\), \(m\)] +
\*SubscriptBox[\(\[Phi]\[Sigma]l\), \(r\)])\) +
\*SuperscriptBox[\(W\), \(N\)]\ \((\[Alpha] + \[Delta]\
\*SubsuperscriptBox[\(P\), \(m\), \(N\)] - \((
\*SuperscriptBox[\(W\), \(N\)] +
\*SuperscriptBox[\(U\), \(N\)])\) -
\*SubscriptBox[\(\[Phi]l\), \(r\)] +
\*SubscriptBox[\(\[Phi]\[Sigma]l\), \(m\)])\)\)\)
D[\!\(
\*SubsuperscriptBox[\(P\), \(m\), \(N\)] \((\[Alpha] - \
\*SubsuperscriptBox[\(P\), \(m\), \(N\)] + \[Sigma] \((
\*SuperscriptBox[\(W\), \(N\)] +
\*SuperscriptBox[\(U\), \(N\)])\) -
\*SubscriptBox[\(\[Phi]l\), \(m\)] +
\*SubscriptBox[\(\[Phi]\[Sigma]l\), \(r\)])\)\) +
W^N (\[Alpha] + \[Delta]
\!\(\*SubsuperscriptBox[\(P\), \(m\), \(N\)]\) - (W^N + U^N) -
Subscript[\[Phi]l, r] + Subscript[\[Phi]\[Sigma]l, m]),
\!\(\*SubsuperscriptBox[\(P\), \(m\), \(N\)]\)]

总之先把精品区《为什么我的代码加了下标（Subscript）就出问题了？》那帖看了……