现在完成体是二语时体习得难点。本研究跟踪103名中国英语学习者76周，四次收集其英语作文语料，考察现在完成体的共时与历时特征。分析表明，76周间，现在完成体频数呈“降—升—降”趋势；三类错误频数均有波动并最终显著下降甚至消除。研究发现与“突显度假说”一致，与“形式先于意义假说”不符。研究认为，二语时体习得是动态复杂系统，时体形式与意义的习得顺序并非恒定，习得水平也并非线性发展，而是具有复杂性和动态系统性。

English Present Perfect is notoriously difficult in L2 tense and aspect acquisition. Having tracked 103 Chinese EFL learners for 76 weeks during which their English compositions are collected at termly intervals, the present study investigates the synchronic and diachronic features of the English present perfect used in the compositions. Data analysis shows that during 76 weeks, frequencies of the present perfect in the compositions exhibit a “fall-rise-fall” trend, and frequencies of 3 types of errors fluctuate and end in significant decline or even disappear. The findings conform with the “Saliency Hypothesis” but disagree with the “Form-Before-Meaning Hypothesis”. The study suggests that L2 tense and aspect acquisition is a complex dynamic system; due to the influences of multiple factors, the form and meaning of L2 tense-aspect are unlikely to be acquired in a fixed order; the proficiency development of L2 tense-aspect exhibits complexity and dynamicality rather than linearity.