According to the superposition model, the air depth at which the shower size reaches its maximum
( 𝑋𝑚𝑎𝑥 ) is sensitive to the mass compositions of cosmic rays, so 𝑋𝑚𝑎𝑥 can be used to identify
the mass compositions and measure the average mean logarithm mass of cosmic rays. The Wide
Field of view Cherenkov Telescope Array ( WFCTA ) as an important part of Large High Altitude
Air Shower Observatory can record the Cherenkov images which can be used to reconstruct
𝑋𝑚𝑎𝑥. The angular distance ( 𝐷𝑖𝑠𝑡 ) between the arriving direction and the gravity center of
the Cherenkov image is related to 𝑋𝑚𝑎𝑥. In this work, the method of the 𝑋𝑚𝑎𝑥 reconstruction
is studied by simulation data, and 20𝑔/𝑐𝑚2 resolution of 𝑋𝑚𝑎𝑥 can be achieved. The ability
of the reconstructed 𝑋𝑚𝑎𝑥 in mass composition identification and the measurement of the mean
logarithm mass is also studied.