Despite the favorable benefits of world tread organization membership on the economy, may also have undesirable adverse effects. So the countries that have infra-structure preparations for this phenomenon and have done sufficient studies before entering World Trade Organization can change threats into opportunity and use advantages to the best. Therefore we have tried to study effects of membership to WTO on a small part of the Iran economy. To this aim by proposing a hypothesis, an economic mathematical model was designed and has been tested. In order to study and analyze the relations among variables, we used annual time series data of 1978-2011 and by using of Microfit software and Johansen convergence method, and it was already known that there is a long term balance relation among variables and estimated the coefficients of model. Gained results of "Johanson-Juselius" tests confirmed long termco-integration relation among the variables of model and the existence of two co-integration vectors. Also in order to study structural failure and the stability of estimated coefficients of model we used "accumulation sum of recursive residuals" test that gained results of this test showed the stability of gained coefficients and finally by estimating models and analyzing of variance, it was cleared that trade liberalization index has effect on dependent variable of model.