Abstract: Ultrasonic phased array testing technique is an advanced ultrasonic nondestructive testing technology. It can achieve controllable synthesized ul trasound beam and focus points by easily exciting each element with independent phase delay. With its dynamic focusing, electronic scanning and S-scanning, the defection result can be improved. Therefore, it has been becoming a focus of ultrasonic testing researching at home and abroad. This paper used a semi-analytical model for the calculation of ultrasonic field based on Rayleigh Integration and Pencil method. Simulation provides the influence on the quality of synthetic sound beam of phased array by probe factors such as element number, distance of adjacent elements. Simulation result is considerably consistent to related theory, which provides the basis for the evaluation and measurement of sound field and the development of high-quality phased array probes