Four groups of superconducting power transmission cables composed of coated conductors with 4.0 mm width and 2 µm superconductor thickness have been designed, including mono-layer, two-layer, four-layer and six-layer cables. In each group, three types of cables have been constructed with gaps of different size between adjacent coated conductors, which are classified into small gap, medium gap and large gap. Moreover, different lateral critical current density (Jc) distributions, specifically a uniform distribution and a trapezoidal distribution with a sloping shoulder, have been assumed while calculating the AC losses of these cables numerically by using a one-dimensional FEM model. Numerical results show that AC losses in mono-layer cables are significantly influenced by gaps between coated conductors as well as lateral Jc distribution, while cables with many layers are hardly affected by them. This proves that small gaps between coated conductors are not absolutely essential to reduce AC losses in multi-layer cables, and a sloping shoulder of the Jc distribution is more allowable in multi-layer cables than in mono-layer cables. The AC loss distributions among layers in six-layer cables are presented and the reasons for different influences of the gap as well as the lateral Jc distribution in mono-layer and multi-layer cables are discussed.