We propose a model of passive mode-locking laser diode based on quantum wells. Numerical results for InGaAlAs/InGaAs/InP heterostructure with 4 quantum wells in active region are presented. The dynamics of the transition to mode-locking has been investigated. It has been shown that mode-locking occurs approximately within 30 ns. The pulse duration was amounted to 2 ps, average output power - to 9.4 mW. The appearance of the second harmonic radiation in the resonator is connected to the insufficient absorber relaxation rate