The paper describes a method of calculating the natural frequency of a complicated piping system which is connected to a reciprocating compressor. Principle of calculation method is the application of Holzer's method generally used in the torsional natural frequency analysis.By multiplying matrix of each element in order, total transfer matrix of the system is obtained, and by applying the end condition, the natural frequency of the system will be gained in such a way that the residue value becomes zero. Calculation program for using a digital computer is completed. Difference of convergence of solution depending on the difference of the choice of lines is also discussed. By this calculation method the natural frequency of any complicated piping system can easily be obtained and great advantages will be found in the design of a piping system which can avoid the damage of piping and equipment due to resonance.