In this paper, our goal is to study the line-soliton solutions of the three-component Kadomtsev-Petrovashvili equation. Its solution also represents the interaction between the three fluid layers. Firstly, we obtain the analytical solutions of thex three-component KP equations, i.e., \(u_0(x, y, t), u_1(x, y, t), u_2(x, y, t)\) , based on the KP theory and the three-component treatment of the \(\tau \) -function. Secondly, we make the following conjectures about the solution structure of the line-soliton on the Grassmannian Gr(N, M). For \(u_0\) , there are N bright soliton solutions when \(y\gg 0\) ; there are \(M-N\) bright soliton solutions when \(y\ll 0\) . For \(u_1\) , there are N bright soliton solutions and N dark soliton solutions when \(y\gg 0\) ; there are \(M-N\) bright soliton solutions and \(M-N\) dark soliton solutions when \(y\ll 0\) . For \(u_2\) , there are 2N bright soliton solutions and N dark soliton solutions when \(y\gg 0\) ; there are \(2 (M-N)\) bright soliton solutions and \(M- N\) dark soliton solutions when \(y\ll 0\) . Again, we verified the accuracy of the conjecture by plotting the images of the soliton solutions on Gr(N, M). In addition, we analyse the rogue waves in the three-component KP equation and briefly explain why the maxima in the line soliton solutions arise.