Temperature triggered chiral nanostructures have been investigated on two-dimensional (2D) surfaces by means of scanning tunneling microscopy. Achiral molecules 1 and 2 tend to self-assemble into strip structures on graphite before heating. However, R and S flower-like structures are observed when heated to certain temperature. The transition temperatures of 1 and 2 systems are 55 and 60 degrees C, respectively. The density functional theory calculations demonstrate that R and S flower-like structures are more stable than strip structures. The coexistence of flower-like structures and strip structures demonstrates the thermodynamic equilibrium. Further, when chiral solvent is added to the sample with other conditions remaining the same, the racemic phenomenon disappears and homochirality emerges. This is an efficient method to control the chirality of 2D molecular assemblies.