Strain engineering of two-dimensional materials provides specific regulation method for the crystal structure, electric transport behavior and hence thermoelectric properties. Since the layer components of the van der Waals heterojunction exhibit discrepant response to strains, it provides a platform for manipulation of emergent electronic and thermoelectric properties. Here, motivated by the promising thermoelectric materials SnSe and its analogue, we design a specific high-promising thermoelectric candidate based on SnSe-SnS heterostructures, focusing on the strain induced asymmetric bonding-transition and its effect on thermoelectric properties. The compressed SnS/SnSe hetero-bilayer shows significantly enhanced anisotropic electrical transport properties, due to depressed carrier scattering rate along the robust weak bonding direction. In this armchair direction, extremely high power factor values (3600 μW/(cm⋅K²)  for n-type and 4000 μW/(cm⋅K²) for p-type) are predicted at ∼10²¹ cm⁻³ at 700 K. We obtain a new state-of-the-art thermoelectric material with extremely high thermoelectric power factor and pave the way for strain engineering of thermoelectric van der Waals heterostructures with robust in-plane weak bonding.