Based on electronic deflection and focusing characteristics, ultrasonic phased array technology is used in flaw detection of girth welds for big diameter long distance pipelines, which overcomes the shortcomings in traditional ultrasonic nondestructive testing. Aimed at the detection requirements, a numerical analysis and modelling of a linear phased array transducer are carried out in this article. Influences of transducers parameters on beam directivity are analyzed. Beam directivity of designed transducer is simulated. Then experiment conditions and test facilities are described. The results illustrate simulation of phased array transducer can optimize its performance, which increases the testing efficiency.