Abstract: In the GB/T 29712-2013 standard, the assessment of indications for ultrasonic testing of welds has two evaluation techniques for acceptance purposes, and present paper mainly discusses the evaluation based primarily on length and echo amplitude of the signal indication. The measurement of the signal indication length adopts fixed echo amplitude level technique, the AL2 (acceptance grade 2) measures probe movement distance of echo amplitude that exceeds H₀-14 dB, and the AL3 (acceptance grade 3) measures probe movement distance of echo amplitude that exceeds H₀-10 dB. The measured distance is the imperfection length of the signal indication. The AL2 or AL3 acceptance levels are determined according to the multiple relationships between the signal indication length, the board thickness and different thickness ranges, and the record levels are equal to the acceptance levels minus 4 dB. By the acceptance levels and record levels, the imperfection echo amplitude of the signal indication is divided into three regions, and they are the qualified zone, the undetermined zone and the disqualified zone. It is believed that this division is a good solution to the problem of defect echo amplitude evaluation based on display. Based on the test of specific example, a detailed discussion was given in present paper to show how to assess the imperfection signal indication in the practical test based on the imperfection length and echo amplitude of the signal indication.