Emittance is an important parameter to evaluate beam quality. With the development of accelerator tech-nology

higher beam quality is demanded. Especially

for the measurement of small emittance

higher solution is re-quired. Based on measurement theory of multi-changing focusing strength

this paper discusses measurement tech-nique and measurement device of the linac of SSRF to enhance accuracy and reliability of emittance measurement

including appropriate use of thin lens

the multi-point least squares fitting

choice of cross section measuring target

and design of software measurement

etc. The stability and reproducibility of measurement results show that the ap-proach can be of significance in emittance measurement of the coming project of free electron laser.