The optical near-field patterns, propagation loss and mode sizes of x-cut $Ti:LiNbO_3$ optical waveguide which was fabricated by Ti-diffusion varying with Ti strip thickness in wet oxygen atmosphere were discussed at optical wavelength 1550nm. As Ti thickness increased from $760{AA}$, the insertion loss of waveguide was decreased. But at Ti thickness $1500{AA}$, mode sizes are widely broadened. The Ti thickness of below $1100{AA}$ and above $1500{AA}$ showed negative effects to propagation loss and fiber coupling. The best Ti thickness for fabricating low propagation loss and good fiber coupling was inferred to be between $1100{AA}-1500{AA}$ in our conditions. And for Ti thickness $1150{AA}$, its propagation loss, horizontal/vertical mode sizes were showed 1.61 dB/cm, $11.9/8.9{mu}m$ for TM, 0.22 dB/cm, $12.0/9.1{mu}m$ for TE respectively.