This study was conducted in perennial alfalfa farm infected by weeds located at Km 7 Hamadan-Tehran road in the spring of 2014 and 2015 in a randomized complete block design with 11 treatments and 4 replications compared with control to investigate the effects of different harvest times of first cutting on the increase or decrease in percentage of dry weight of weeds and also alfalfa in second cutting. Treatments of this research were different harvest times in different stages of flowering in terms of percentage including: first harvesting in 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50% of flowering in Alfalfa farm. In both years, the treatments were performed only in the first cutting and their effects were evaluated on the first and second cutting. In the second cutting the harvest time took place in 50% of flowering. Sampling was performed to determine the dry weight of alfalfa and also density and dry weight of weeds. The results showed that when the weed infestation is high in established alfalfa farm, early harvest in the first harvesting can significantly reduce the percentage of weeds and also the positive effects of it can be observed in second harvesting, as if early harvest increased the percentage of dry weight of alfalfa and a wide range of weeds was controlled. The final results showed that alfalfa harvesting in lower percentages of flowering led to better control of weeds.