Nodeless superconductivity in the topological nodal-line semimetal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">CaSb</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

${\mathrm{CaSb}}_{2}$ is a topological nodal-line semimetal that becomes superconducting below 1.6 K, providing an ideal platform to investigate the interplay between topologically nontrivial electronic bands and superconductivity. In this work, we investigated order parameter of by measuring its magnetic penetration depth change $\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}(T)$ down 0.07 using tunnel diode oscillator based technique. Well inside state, shows exponential activated behavior, provides direct evidence for nodeless gap. By analyzing temperature dependence depth, superfluid density specific heat, find both can be consistently described two-gap $s$-wave model, in line with presence multiple Fermi surfaces associated distinct Sb sites compound. These results demonstrate fully gapped superconductivity constrain allowed pairing symmetry.