Small and medium enterprises (SME) in all societies play a very important role in improvement of economic indicators especially employment. Therefore, supporting these businesses for instance bank loan, can have many positive effects on the entire economy. However, the occurrence of shocks such as spreading of the Covid-19 virus causes high credit risk and some problems for these supports. So, this research has investigated the impact of the Covid-19 virus epidemic on the performance of bank loan to small and medium-sized companies in Iran. In this study, the data of the amount of lending by Iranian banks to SMEs for the period of December 2019 to December 2021 was collected on a monthly basis. Changes in data was affected by the growth of the number of people infected with the virus during this period and it has been analyzed by the Markov regime transfer method. The results showed that when the dependent variable is in its high regime, the growth of the number of people infected with the Covid-19 virus does not have a significant effect on the system. but in the low and medium regime, this variable has a negative and significant effect on the amount of bank loan to SMEs in Iran. In addition, the impact of some variables such as the growth of the exchange rate and the inflation index on the lending performance of banks was also considered during the pandemic.