In clinical assessment or sports exercise.it is common that a subject is required to repeat a specific per-formance so that a stable movement pattern is obtained and analysed.In practice,however,the trials done by a sub-ject vary more or less,depending on the psychological or physical conditions.Some of the trials can be used as rep-resentatives of the stable movement pattern,and some not.Therefore,there is a demand for a new method to identify which trials/curves are similar.The traditional methods used to assess curve similarity are not perfecfly suitable for the case where there are only a few of trials available.This study proposes a similarity-distance coefficient to assess the similarity of curves/trials.A group of designed curves are used to validate the coefficient.The results show that given joint kinematic data during gait as examples,tlle proposed coefficient call be used to quantitatively evaluate the similarity of trials,and thus find which trials would be representative(S)for the gait investigated.The proposed method could be applied in various situations where repeat movements have to be measured and analysed.