The accurate analysis of the stiffness and deflection of steel and concrete composite beams is complicated due to the possible interface slippage. Exact procedures for static linear-elastic analysis of composite beams with interlayer slip were presented. An efficient second-order algorithm using two second-order ordinary differential equations in terms of interlayer slip and deflection was established to calculate the interlayer slip and the deflection of composite beams, and exact closed-form solutions for four Euler boundary conditions were then derived according to their boundary conditions. The internal forces of composite beams with interlayer slip were also derived. Compared with the higher-order algorithm, the second-order algorithm can simplify the calculation of the deflection of composite beams with interlayer slip and give relatively comprehensive solutions.