In this study, the effect of the nozzle pressure ratio on the divergence efficiency of a linear aerospike nozzle has been investigated experimentally and numerically. To compare with conventional nozzles, a conical nozzle with the same design conditions as the Aerospike nozzle was used. The used nozzles are the type of plate nozzles, and the supersonic flow coming out of them was investigated by Schilleren's imaging technique. The comparison of Schilleran's experimental images with the results of the numerical solution showed the accuracy of the three-dimensional numerical simulation. The effect of the nozzle pressure ratio on the distribution of the supersonic flow areas of the nozzle outlet was observed. The results showed that the deviation of the flow from the axial mode with increasing the pressure ratio from 3 to 9 for the conical nozzle is three times more than the Aerospike nozzle. Also, by using the divergence efficiency relationship, it was shown that the efficiency of the Aerospike nozzle has fewer changes with changes in pressure ratio, and in values much lower than the design pressure ratio, it has a favorable efficiency of about 98%. The adaptability of the linear aerospike nozzle in changes in the pressure ratio is greater than that of the conical nozzle, so that reducing the pressure ratio by half of the design pressure ratio in the conical nozzle reduces the divergence efficiency by 10%, while this amount for the aerospike nozzle is less than 3 percent.