Modulation spectrum simulation is important for the simulation of ship radiated noise, because the modulation spectrum contains abundant characteristics of ship target. To satisfy various research requirements for the simulation of ship radiated noise's modulation spectrum, reconstruction method is utilized based on measured ship radiated noise. The generated modulation spectrum is similar to the measured one with good fidelity. The modulation envelopes are simulated by a pulse stochastic process, where pulses are governed by a set of parameters. Among them, the rotation period, blade number, pulse width and modulation depth of the propeller are obtained with demodulation analysis and time domain analysis on the measured signal. The modulation pulses' amplitude parameters can be got by looking up in a correspondence table between modulation pulses' amplitude data and modulation harmonic spectrum lines, which is generated by simulations and data processes. Simulation results show that frequency and power order of the first group of modulation harmonic spectrum lines are well maintained.