Hydrate crystals growth on the surface of methane bubble (hydrate film) in pure water was studied by using a high-pressure visible microscope under the conditions of subcooling Δ

T

= 5.44–13.72 K and methane concentration difference Δ

C

= 2.92–8.19 mol·L

-1

. It was found the hydrate film is porous and the hydrate crystals grow towards the liquid phase on the film substrate. The crystal morphology and growth rate are affected by Δ

T

and Δ

C

. When Δ

T

8.82 K and Δ

C

4.12 mol·L

-1

the hydrate grows into scattered columnar crystals

and the axial growth rate of the crystal gradually decreases. When Δ

T

8.82 K or Δ

C

4.12 mol·L

-1

the hydrate crystals grow in dendritic shape

and the axial growth rate increases first and then decreases. The perimeter and area of the growing hydrate crystals were measured

and the fractal dimension of hydrate crystal under different Δ

C

and Δ

T

was calculated. The results show that the fractal dimension of columnar hydrate crystal is greater than 3. When 3.87 mol·L

-1

Δ

C

4.20 mol·L

-1

and 7.4 K Δ

T

8.8 K

the fractal dimension of columnar hydrate crystal is greater than 4; The fractal dimension of dendritic hydrate crystal is less than 3. When Δ

C

4.77 mol·L

-1

Δ

T

8.52 K

the fractal dimension of dendritic hydrate crystal is less than 2.