The sentence 'let him understand' is correct and usable in written English.
You can use it when you want to communicate a goal or request that someone else understand something. For example: "I want to explain this concept in depth, so let him understand."
Sent by the weather bureau to establish a meteorological observatory in the frontier town of Anchorage in 1915, he's obsessed with finding a formula that will let him understand and predict the weather.
A concert impresario and record label head who fought constantly for integration — both on the stage and in the audience — Granz was also gifted with an ear that let him understand how to deploy a given artist's talent or determine who might be suitably paired with whom.
Despite the fact that he never graduated from high school, Felton is in many ways an intellectual, and he wanted to be able to intellectualize his own racial anxiety, to find a coherent philosophy that could let him understand his own place in the divided racial world that he saw around him.
"I needed to let him understand where his problems were.
And when this occurs to us we are moved to deal kindly with him, to bid him be of good cheer, to let him understand that we are also fighting a battle.
I posed the question right back to him to let him understand the chances of that".
In the familiar version of the novel, a puzzling line appears during a scene, late in the book, in which the State's Attorney tries to intimidate Bigger by letting him understand that he has information about other crimes and misdeeds Bigger has committed, including, he says, "that dirty trick you and your friend Jack pulled off in the Regal Theatre".
Let him also understand as to how hard you worked to resolve such an important problem.
Suggestion: If your boyfriend is angry with his mother, even for reasons you agree with, listen compassionately, console, comfort, and let him know you understand why he's upset.
Experts suggest that acknowledging negative emotions allows them to dissipate faster than denying them, so if your teen boy is feeling sad or angry (and these things will happen!), let him know you understand he's experiencing those emotions.
"Teenagers," says Hiller, "sometimes respond positively if they think you can see things as they do, so try to let him know that you understand that his anger is unpleasant for him too and that you want to help.
