In this article, we focus on the following fractional Choquard equation involving upper critical exponent $$\begin{aligned} \varepsilon ^{2s}(-\varDelta )^su+V(x)u=P(x)f(u)+\varepsilon ^{\mu -N}Q(x)[|x|^{-\mu }*|u|^{2_{\mu ,s}^*}]|u|^{2_{\mu ,s}^*-2}u, \ x \in {\mathbb {R}}^N, \end{aligned}$$where \(\varepsilon >0\), \(0<s<1\), \((-\varDelta )^s\) denotes the fractional Laplacian of order s, \(N>2s\), \(0<\mu <N\) and \(2_{\mu ,s}^*=\frac{2N-\mu }{N-2s}\). Under suitable assumptions on the potentials V(x), P(x) and Q(x), we obtain the existence and concentration of positive solutions and prove that the semiclassical solutions \(w_\varepsilon \) with maximum points \(x_\varepsilon \) concentrating at a special set \({\mathcal {S}}_p\) characterized by V(x), P(x) and Q(x). Furthermore, for any sequence \(x_\varepsilon \rightarrow x_0 \in {\mathcal {S}}_p\), \(v_\varepsilon (x):=w_\varepsilon (\varepsilon x+x_\varepsilon )\) converges in \(H^s({\mathbb {R}}^N)\) to a ground state solution v of $$\begin{aligned} (-\varDelta )^sv+V(x_0)v=P(x_0)f(v)+Q(x_0)[|x|^{-\mu }*|v|^{2_{\mu ,s}^*}]|v|^{2_{\mu ,s}^*-2}v, \ x \in {\mathbb {R}}^N. \end{aligned}$$