Aiming at the problem of tilt control in coherent beam combining of laser array, a tilt control method, of which the evaluation function is based on second order moment of combined laser beam, is proposed. The performances of the tilt control method are investigated theoretically and experimentally. In the theoretical study, adopting the second order moment of the combined beam as the evaluation function, the tilt control process of 7 laser beam is simulated based on stochastic parallel gradient descent algorithm. In the experiments, a coherent beam combining system of 7-channel fiber array is built and an adaptive fiber collimator is used as the tilt-control device. Adopting the stochastic parallel gradient descent algorithm, the closed-loop operation of tilt control is achieved with the second order moment of the combined spot as the evaluation function. The theoretical and experimental results show that the tilt control method based on the second order moment of laser beam has great potential on coherent beam combination.