In this paper, a new blocked tandem queueing model is given and analysed. The arrival process to this queueing model is Poisson with parameter 𝜆. There is one service unit at the first stage of the system, and the service time of this unit is exponentially distributed with 𝜇1 parameter. There are two parallel service units at the second stage, and the service time of these service units are exponentially distributed with parameters 𝜇2 and 𝜇3. No queue is allowed at the first stage of the system. Upon completing service at the first stage, a customer proceeds to the second stage if at least one of the service units at the second stage is available. If both service units at the second stage are busy, the customer blocks the service unit at the first stage, which results in loss. The most important measure of performance of this queueing system is the loss probability 𝜋𝑙𝑜𝑠𝑠 . First of all, the state probabilities of the system are obtained and then using these probabilities, the steady-state distribution of the system is obtained. Transition probabilities of the system are calculated by using steady-state probabilities, and finally an equation is obtained for 𝜋𝑙𝑜𝑠𝑠 in terms of transition probabilities. Furthermore, another measure of performance, the mean number of customers, is obtained in terms of transition probabilities. Since the Equation for 𝜋𝑙𝑜𝑠𝑠 is very complex, a numerical method is used to calculate the minimum 𝜋𝑙𝑜𝑠𝑠 probabilities. After numerical optimal 𝜋𝑙𝑜𝑠𝑠 calculations, a simulation of the queueing system is done, and it is seen that the obtained numerical 𝜋𝑙𝑜𝑠𝑠 values tend to simulation results.