In an InGaAs/(110)InP, a CuAu-I type ordered structure is formed during growth with a propagation of two-monolayer steps (2-MLSs). The numerical calculation with an empirical interatomic potential has suggested that the ordered InGaAs clusters are stabilized at kink edges of the 2-MLSs. We confirmed that In and Ga adatoms preferentially occupy the upper and lower sites at a kink of 2-MLS, respectively. This explains that the CuAu-I type ordered structure which is made of alternately stacked In- and Ga-rich (110) planes is formed by propagation of the 2-MLS with kinks. Our Monte Carlo simulation using the ordering model showed that the ordered structure is actually formed at the growth temperature (~700 K).