Efficient turbine blade cooling structure design with high cooling effectiveness and low cooling loss is essential for improving the efficiency of turbomachines. This paper designs a new cooling structure combining external film cooling and internal convection cooling for a 1/2 scaled down gas turbine vane. The superheated steam replaces the traditional compressor air as coolant for the internal convective cooling. Wind tunnel experiments are conducted on a linear turbine cascade at exit Mach numbers of 0.9, and exit Reynolds number of 1.2 x 10(6), in order to study the cooling effectiveness of this cooling structure. Then the cooling entropy creation due to inevitable cooling losses (including internal friction and heat transfer losses and external heat transfer and mixing losses) of air cooling and steam cooling is estimated and discussed. It is found that, the cooling effectiveness of the test vane with newly designed cooling structure is high (approximately 0.8) and uniformly distributed. The entropy creation of external air cooling due to external mixing is higher than the heat transfer, and for the steam convective cooling, the entropy creation due to internal friction is much higher than heat transfer in the cooling process. (C) 2014 Elsevier Ltd. All rights reserved.