Mechanical properties of composite solid rocket propellant are one of the most important propellant specifications and also improvement of the interfacial interactions between bonding agents and solid particles is a demand for composite solid propellants in order to withstand stresses produced due to various loading conditions, changes in environmental condition, transportation and handling. In this work, long chain bonding agent prepared from the reaction of fatty monocarboxylic acid and dicarboxylic acid with methyl aziridinyl phosphine oxide (MAPO) to form (MSA) bonding agent which is improved the mechanical properties especially strain value corresponding to stress value which gives the highest value in formulation B1 but with low yield properties. Also using an percentage of MAPO as a mixed bonding agent in order to increase the yield properties of the propellant has a significant effect on mechanical properties as giving high value of Youngs modulus and good strain value with the percentage of 0.1% of MAPO and 0.2% of MSA then by changing the curing agent using IPDI instead of HMDI also gives a remarkable mechanical properties as high strain corresponding stress with a good value with modulus in formulation CI2.