Abstract: The present study was to construct three vocabulary tests at junior school level that could be used for measuring the student's lability of word omeaning comprehension.The three tests were constructed of 143 words multiple-choice items and administered to about 3000 students. The statistical item analysis and the test of goodness-of-fit of the 2PL model showed 90% vocabulary items could be used for IRT analysis. IRT analysis of the item responses was carried out separately for each test and estimated item parameters were equated utilizing the anchor items included in all the tests, the mean discrimination parameter of each grade was 0.61(grade7), 0.59(grade8),0.55(grade9); the mean difficulty parameter was - 1.61, - 1.30, - 0.56 respectively.

Key words: vocabulary test, 2PL model, test equating, test information