The beam direction of the phased array antenna changes dynamically. Its electromagnetic emission characteristics show significant statistical laws, and the resources required for analysis and testing are numerous. In this paper, polynomial chaos expansion (PCE) is used to explore the statistical characteristics of the two-dimensional planar phased array antenna’s emission. The objective function of the phased array antenna is determined according to the pattern product theorem, and PCE is used to establish an equivalent surrogate model of the array’s emission characteristics. The paper starts from the phased array antenna composed of ideal point sources, and considers two typical cases that the main beam direction obeys the uniform distribution and the normal distribution. The statistical characteristics of the equivalent surrogate model are obtained by computer simulation. The results of the traditional Monte Carlo (MC) method are used as a reference to evaluate the effectiveness and reliability of the PCE method. At the end of the paper, the situation that the beam direction of the dipole phased array antenna obeys two typical distributions is briefly discussed. The comparison of simulation results shows that the PCE method can greatly reduce the sampling numbers of calculation while ensuring the accuracy of the results, and significantly improve the efficiency of analysis and testing.