Abstract: When a natural gas network is done off-line numerical simulation, every pipeline needs be distributed initiatory flow as the initiatory value of iterative computation. A mathematical model of initiatory flow distribution is established according to the peculiarity that the pipeline flow state is usually at drag square area, and a calculate program is written out with C++. The calculating and analyzing of instance show that computing every pipeline initiatory flow with the method of minimum square summation need not handwork preliminary distributing initiatory flow and assuming flowing direction of every pipeline fluid. Mean while, the computed initiatory value meets the true value, the convergence velocity of numerical calculation is greatly improved.