Based on the model of the Maxwell's equations coupled with the rate equations of electronic population, the lasing threshold of optical modes in partially random media is analyzed using the finite difference time domain method. The characteristics of random laser can be described by some factors, such as the strength of randomness, size of medium,etc.,which determine the lasing threshold in random medium. The simulated results show that one or more lasing modes appear when the pumping rate Pr increases beyond the threshold, and the number of modes will increase with random strength and size of medium. In addition, the simulated results demonstrate that the lasing threshold value will attain the minimum value under certain random strength and size of medium, which is at variance with the theoretical result in one-dimensional completely random medium. Such properties of the medium show potential advantage in future application for optical integration.