We report quantitative nanocrack formation upon adjusting the mechanical tensile strain applied to a Pd thin film on an elastomeric polydimethylsiloxane (PDMS) substrate and its detection properties for H-2 gas in air. Nanocrack formation in Pd/PDMS substrates was controlled through the application of tensile strains that varied in the range 30-120 % during mechanical stretching/compression. This method can be used to modulate nanocrack formation along both the x- and y-axes over a large area. Increasing the applied tensile strain to 90 % induced the appearance of horizontal cracks along the y-axis in addition to an increased number of vertical cracks along the x-axis. When the strain reached 120 %, ordered nanocracks abundantly propagated on the Pd surface in both the directions. Gas detection properties were dramatically enhanced, with a very low detection limit of 50 ppm H-2 in air observed for 120 % strain. This was attributed to the large surface area in the Pd nanocrack pattern, which readily allowed for volume expansion. These results provide a simple mechanism for controlling the detection properties of H-2 gas sensors with low detection limits in air.