Interlanguage is an emerging linguistic system that has been developed by aleamer of L2 who has not become fully proficient but is approximating the targetlanguage, while at the same time preserving some features of their L1. As a result ofthe influences coming from their existing linguistic system of L1, subjects, inconducting conversations in L2 classes, reveal numerous errors with characteristicfeatures identifying their L2 proficiency.　　 Thus, this paper focuses on the errors in learners interlanguage, and nativelanguage transfer, which influences the development of the learning process of thetarget language. This paper aims at probing into the features of learners interlanguagethrough analysing their errors, which is essential to identify their target languageproficiency from locating the position on the interlanguage continuum. By analysingthe reoordings of task-based conversations conducted by 30 freshmen and sophomoresin USTC, this paper solves the three questions: 1) what are the features of thisparticular level (non-English-major college freshmen and sophomores) on thecontinuum; 2) how are L2 learners at this particular level affected by their mothertongue; 3) how can these phenomena be explained according to interlanguage theories.Moreover, seven types of errors and their features, revealing the status of theirinterlanguage, have been discovered to identify the phase of the subjects.　　 Furthermore, a comparison with recognized advanced EFL learners is alsoapplied in the experiment as verification. As this paper lays its emphasis on theanalysis of practical language materials, it might be beneficial for the SLA research.In the last part of the paper, effective measures and ways are sought so as to providelearners with more focused, tailored and effective instructions in SLA study, whichalso arises further research questions to further improve and upgrade SLA pedagogyboth theoretically and empirically.