Abstract: Based on the simplified P₃ (SP₃) method, a SP₃ analytic function expansion nodal code was developed under three different partial current expressions. The numerical test of the code was carried out and the accuracy of the three partial current expressions was compared. The numerical results show that the pin-by-pin transport calculation based on the SP₃ analytic function expansion nodal method can obtain high accuracy of the pin power. Among the three different partial current expressions, Marshak’s expression has the highest accuracy while the other two expressions are more conducive to code’s algorithm simplification and parallel algorithm design.