Diamondene has received the attention of scientists recently because of its brilliant physical properties. But, owing to the limitations of current technology, defects are indispensable during the production of diamondene. In this work, the effect of boundary cracks on the tensile properties and damage mechanism of diamondene are investigated by using molecular dynamics method. The results show that the crack leads the tensile properties of diamondene to be weakened, and the elastic modulus, cracking strain, and cracking stress of diamondene containing a boundary crack to become less than those of diamondene without cracks. As for the failure mode, the damage of crack-free diamondene starts near the mobile end, while the damage of diamondene with a boundary crack starts at the crack tip. After the cracking strain has been reached, the crack will form a penetration rupture without further loading and the crack-free diamondene completely loses its load-bearing capacity. However, in diamondene with a boundary crack, the load still needs adding, and the crack will form a penetration crack after the cracking strain has been reached through several extensions. Furthermore, the tensile properties of diamondene with a boundary crackare strongly dependent on temperature, and decrease significantly when the temperature increases. Changes in the location, length and direction of cracks can cause the tensile properties and damage mechanism of the crack-containing diamondene to change.