Recently, the LHCb Collaboration reported three $P_c$ states in the ${J/psi}p$ channel. We systematically study the mass spectrum of the hidden charm pentaquark in the framework of an extended chromomagnetic model. For the $nnncbar{c}$ pentaquark with $I=1/2$, we find that (i) the lowest state is $P_{c}(4327.0,1/2,1/2^{-})$ [We use $P_{c}(m,I,J^{P})$ to denote the $nnncbar{c}$ pentaquark], which corresponds to the $P_{c}(4312)$. Its dominant decay mode is $Lambda_{c}bar{D}^{*}$. (ii) We find two states in the vicinity of $P_{c}(4380)$. The first one is $P_{c}(4367.4,1/2,3/2^{-})$ and decays dominantly to $N{J/psi}$ and $Lambda_{c}bar{D}^{*}$. The other one is $P_{c}(4372.4,1/2,1/2^{-})$. Its dominant decay mode is $Lambda_{c}bar{D}$, and its partial decay width of $Neta_{c}$ channel is comparable to that of $N{J/psi}$. (iii) In higher mass region, we find $P_{c}(4476.3,1/2,3/2^{-})$ and $P_{c}(4480.9,1/2,1/2^{-})$, which correspond to $P_{c}(4440)$ and $P_{c}(4457)$. In the open charm channels, both of them decay dominantly to the $Lambda_{c}bar{D}^{*}$. (iv) We predict two states above $4.5~text{GeV}$, namely $P_{c}(4524.5,1/2,3/2^{-})$ and $P_{c}(4546.0,1/2,5/2^{-})$. The masses of the $nnncbar{c}$ state with $I=3/2$ are all over $4.6~text{GeV}$. Moreover, we use the model to explore the $nnscbar{c}$, $ssncbar{c}$ and $ssscbar{c}$ pentaquark states.
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